AmericanLongRifles Forums
General discussion => Gun Building => Topic started by: recurve on February 10, 2019, 07:08:11 AM
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How deep into the barrel should a breach plug be to be considered safe. What depth of the threads 3/8 ,1/2 etc.... How many threads are considered safe for a .50 7/8 barrel (Gmtn) hook breach for 70 grns -100 of powder .490-495 ball?
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If you will do a Google search for "maximum thread strength" , you will find a lot of information.
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most all the barrels I use are fitted with 1/2" plugs. Colerain has something closer to 5/8". The old timers often went with a course threaded 3/8" long plug. You roll the dice and plays your game.
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I have several friends that are engineers. They told me that 3 full threads is the maximum strength. That is full threads. Remember it takes many more times the pressure to blow the plug than it does to blow the barrel.
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I learned many years ago in my millwright training, that thread engagement length the same as the thread diameter is required for maximum strength.....i.e....5/8 dia. threads should engage at least 5/8 in length to have full strength. I will continue to comply with that rule with any threaded applications I do.
I see no reason to reduce any threaded engagement below minimum full strength engagement any where reliance on the threads' strength becomes a safety issue.
just sayin'
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Minimum safe breach? - ???? is this known? - size of threads vs. barrel diameter, # of threads engaging, depth of engagement, barrel and/or breech material?
Now, I am not suggesting this is 'safe', however the plug didn't blow.
As you can see in the text, the three threads engaging the barrel's threads, had .0025" to .0225" engagement. Now the remaining thread is also mildly engaging
except for where the vent met the plug. 3 drams of 3F was the only charge used in this made in India 'piece'. The breech was 1.0", bore .750".
(https://i.ibb.co/syd4pt4/Pictures-006.jpg) (https://ibb.co/f4zWVQW)
I returned this musket and the outfit in Ontario said they had a Gunsmith proof it and it was fine, using 200gr. of "powder" and 2 balls. Go figure.
BTW- the hole was only in the middle at the muzzle and at the breech. I cut 4" off the muzzle and the bore was one-sided with .020" wall on one side, .050" on the other.
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Recurve: When it comes to barrel wall thickness and breech plug depth there is no excuse to cut corners! I have always used the formula of : breech plug dia. = the depth of thread into the barrel and add at least 1/8" to the depth. So if the plug is 3/4X16 then the depth into the barrel is at least 3/4" and NO less! It doesn't matter what an "old timer" did he isn't around any more to explain himself! If you have ever witnessed a breech failure you will never use only the minimum threads or wall thickness again! I have witnessed several breech failures and but for the Grace of God I and no one else was seriously hurt. .50 X 7/8" AF at the breech is already too thin in terms wall thickness according to my thinking. If I were you I would use my method of breeching for your project. ( See attached). Hugh Toenjes
(https://i.ibb.co/ygjf4xw/H-Toenjes-breeching.jpg) (https://ibb.co/MP02BJY)
virtual dice roll (https://freeonlinedice.com/)
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I have several friends that are engineers. They told me that 3 full threads is the maximum strength. That is full threads. Remember it takes many more times the pressure to blow the plug than it does to blow the barrel.
This is true. I worked structural components for the Air Force 41 years and while building fixtures to machine parts with limited room this subject came up quite often. Engineering always had the same answer; 3 full threads gives you the maximum strength.
But I think other things like thread fit, 3A or 2A or even looser will reduce thread engagement to the point where it becomes weaker. Personally I've never tested the theory as I always managed to get more than 3 threads deep.
I don't think 3 threads deep with sloppy thread fit is the place for me to shoulder and fire a rifle and just hope.
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I agree with Hugh in at least one aspect. It doesn't matter what the old timers did. Who knows what their failure rate was, Bet it was way more than ours today. I often breech barrels the same way Hugh does. It gives great strength and allows the pan to be set back. I am now working on a double flint French pistol. the breech plugs are 1" long and 20 tpi. Gold liners will go through the hollowed out plugs. The gun will probably never be fired but if so it will not fail. 28ga. A plug either has to strip all the theads or turn sideways to come out. Most modern barrels are 8 times more likely to fail than the plug is. Because the pressure on the barrel is ABOUT 8 times the pressure on the plug. most of the fear over breech plugs is caused by the fact that your face is behind it.
Around here we have a guy called bad hand. He loaded one full load on top of another and fire his gun because he was too lazy to pull the load. It turned the barrel to shrapnel but the plug was intact. His face is ok his hand is not. that is reallty.
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I don't understand why someone would even go less than the full diameter of thread engagement length. who cares about period correct or accurate copy of a particular gun when the issue is your safety. a plug engaged by three threads or a full diameter isn't going to make a gun look ugly or great. i'd rather have a gun that I know is safe ( or at least know I did everything I could to be safe) than a gun that copies what someone thought was safe 200 years ago.
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Well, I guess just for safeties sake I'll start going with 12" of thread.
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Friends,
I know I am going to bore some of you with some actual engineering but I can't help myself.
The "3 full threads" rule comes from the SAE standard for threaded components. SAE standard nuts are thick enough to give you 3 full class A threads because those three full threads are as strong as the a rod having a diameter equal to the minor diameter for the male threaded component. Making the nut thicker achieves nothing because the limiting factor is the tensile strength of the male component. This is NOT the threading system in use with a breach plug. With a breech plug the threads should be as strong as the barrel wall. So we take the cross-sectional area of the barrel immediately in front of the breech face and compare it to the thread area (thread minor diameter multiplied by pi, multiplied by thread length). If the thread area exceeds the barrel cross-sectional area then the shear force necessary to cause failure of the breech plug threads is greater than the tensile force necessary to cause the barrel wall to fail; the breech threads are stronger than the barrel wall. Of course, this ASSUMES that the barrel and the plug are mad of the same quality steel.
For my double gun I used a breech very much like the one that Hugh illustrated. Six full threads equaled the barrel wall cross-sectional area.
Best Regards,
JMC
John Cholin
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I suppose back in the good old days they just blew their customers up at will and no one cared? How many of the thousands of barrels breeched at least 1/2 inch deep by the barrel maker or a competent machinist/gunsmith have failed? I think if it was a problem then we all would have breech plugs popping out like champagne corks. It just isn't a problem in my opinion.
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I have never seen evidence of a failed breech plug but I have personally seen a failed barrel at the face of a Breech plug. I don’t know the science or engineering of thread strength but I believe in it. I worked in nuclear power plants for several years, the 3 thread minimum for maximum strength is a rule used in threading applications for that industry. I would be way more concerned about barrel wall thickness at the end of threads than that of a failure of the breech thread engagement. I believe that is why many of the early barrels are heavy at the breech and taper away from the breech. The long and slender barrels that are being made today scare me much more than thread engagement.
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the OP's question was about the strength of thread engagement distance, not barrel wall thickness. if the barrel wall is not thick enough to maintain strength,...... it doesn't matter how many threads are engaged.
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I learned many years ago in my millwright training, that thread engagement length the same as the thread diameter is required for maximum strength.....i.e....5/8 dia. threads should engage at least 5/8 in length to have full strength. I will continue to comply with that rule with any threaded applications I do.
I see no reason to reduce any threaded engagement below minimum full strength engagement any where reliance on the threads' strength becomes a safety issue.
just sayin'
This is a really neat subject. I agree and always use the above statement, when you are putting a pipe bomb next to your face, you just can't be too careful. Safe is always better than sorry.
There is always more to the story....The % of thread engagement is a factor as is the quality and temper of the steel. The other important point is the shape of the plug, if it is drilled or cast with a channel to the nipple, look out, as the plug will only be as strong as the area that is not channeled (Drilled or cast) under the threads. I had one blow the back out of the plug and after further examination discovered that there was only 1/8" of thread contact that was not undercut. More is better.
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Well, I guess just for safeties sake I'll start going with 12" of thread.
don't you think that would look kind of silly Mike ?.....I know your post sure looks silly.
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I have several friends that are engineers. They told me that 3 full threads is the maximum strength. That is full threads. Remember it takes many more times the pressure to blow the plug than it does to blow the barrel.
Jerry,
Engineers up here in Washington use the formula that max thread strength is reached once the length of engagement equals diameter.
David
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This is an interesting thread with lots of room for thought. I am not an engineer and claim no expertise. But, I do think there are many variables. I used to race motorcycles, and when building high out put engines, the torque placed on threads was CRITICAL. Some nuts, under a great deal of stress, required only a few foot pounds of torque to achieve maximum strength, and they usually only had 3-4 threads engaged. Too much torque gave guaranteed failure. That is for you engineer types to figure, I just followed the specs religiously. Personally, I would prefer shorter plug, say 1/2 inch, properly torqued, to one even longer that has been way over torqued. You lose much of the strength of the threads if you are tightening them up to the point you need a 24 inch breaker bar to tighten them. It might be helpful if someone had some evidence based data on this for breechplugs.
Another variable, which does not address the OP's question, is, in my opinion, we use a lot more powder than they did in the old days. People today routinely shoot 100gr+ loads in 50 calibers, I don't think those were normal loads back in the day.
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This is an interesting thread with lots of room for thought. I am not an engineer and claim no expertise. But, I do think there are many variables. I used to race motorcycles, and when building high out put engines, the torque placed on threads was CRITICAL. Some nuts, under a great deal of stress, required only a few foot pounds of torque to achieve maximum strength, and they usually only had 3-4 threads engaged. Too much torque gave guaranteed failure. That is for you engineer types to figure, I just followed the specs religiously. Personally, I would prefer shorter plug, say 1/2 inch, properly torqued, to one even longer that has been way over torqued. You lose much of the strength of the threads if you are tightening them up to the point you need a 24 inch breaker bar to tighten them. It might be helpful if someone had some evidence based data on this for breechplugs.
Another variable, which does not address the OP's question, is, in my opinion, we use a lot more powder than they did in the old days. People today routinely shoot 100gr+ loads in 50 calibers, I don't think those were normal loads back in the day.
Col Hanger talks of 1/2 ball weight of powder during the Revolution, 90 grains from a 50 cal. So heavy charges were not unknown.
When Gen Fraser was shot at second Saratoga at 300 yards I doubt the shooter was using 50 grains of powder.
I generally use the cupped breech with the vent in the breech. This was done by the British when patent breech was not used.
The cupped breech will also give a velocity increase over a flat breech. Or so I have been told, never tested it. would have to breech a barrel flat then shoot it with a cupped breech to prove this and its not worth the trouble to me.
I tend to use the 1/2 to 5/8" plug. Though I know that in a 54 caliber 4-5 threads with 3/4 plug will stand any pressure likely the be generated in a ML even with a very stiff proof. 600+ gr of lead and 200 gr of strong powder. But we must also assure the plug is seated properly against a shoulder.
This is a 58 cal with a cup. Note the grooves show on the breech face.
Dan
(https://i.ibb.co/4MvWpbt/UNADJUSTEDNONRAW-thumb-3ae5.jpg) (https://ibb.co/WF8nfr5)
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Well, I guess just for safeties sake I'll start going with 12" of thread.
don't you think that would look kind of silly Mike ?.....I know your post sure looks silly.
It was meant to be silly. It's called sarcasm. You guys can sure find a lot of ridiculous stuff to worry about. ::) If a 1/2" long breech plug was dangerous 90% of everybody on this forum would be dead by now. ::) Now lets move on and speculate again for eight pages how dangerous 12L14 is...that's always fun.
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Here is the breech plug in my rifle green mtn barrel 36 inch length (internal 351/2) but the touch hole is 1/4 x28 and is located just over 3/8 inch from the breech end of barrel. the plug is 1/2 and is filed to 3/8 on the touch hole side . The rifle has a date 1-91
1 is this safe ?
2 the builder has marked max load 100 3fff ?
3 can/should this be replace(and at what cost)?
(https://i.ibb.co/9ZwVz6k/DSC02968.jpg) (https://ibb.co/km39kjs)
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(https://i.ibb.co/MsWbGK9/DSC02970.jpg) (https://ibb.co/80TJdGX)
(https://i.ibb.co/x3g78cr/DSC02969.jpg) (https://ibb.co/R76D4MJ)
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Well, I guess just for safeties sake I'll start going with 12" of thread.
Mike,
That means your long barreled guns will now have 10ft barrels😂!
AsMs
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"Well, I guess just for safeties sake I'll start going with 12" of thread."
If you keep your lock and touch-hole in alignment with each other, and you have a 12" plug, I think you can attach your tang to you buttplate return. :-) Hah, hah! Enjoyed the dry humor Mike.
God Bless, Marc
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Here is the breech plug in my rifle green mtn barrel 36 inch length (internal 351/2) but the touch hole is 1/4 x28 and is located just over 3/8 inch from the breech end of barrel. the plug is 1/2 and is filed to 3/8 on the touch hole side . The rifle has a date 1-91
1 is this safe ?
2 the builder has marked max load 100 3fff ?
3 can/should this be replace(and at what cost)?
Others think notching the plug face is OK. I disagree and would never do it. It defeats the compression seal at nose of the plug. This one also has too few threads. You have no idea how well the tapping and threading was done. There is a difference in strength between well fitted tight threads and loosie goosie ones done freehand with a hardware store tap and die.
When I build a rifle safety is paramount. I would not trust that plug in a rifle owned. I would never sell such a rifle. I am a worrier and obsessive about doing good work. Hurting somebody because of shoddy work is a chance I will not take.
As much as I hate long plug threads with a chamber that would fix this. Ignore the existing threads strength wise. Run the threads 3/4"+ up past the liner. Be sure there is 5/8" of clean threads. Make a new long plug. Install the new liner like Hugh CVA or Pedersoli, in the side of the plug threads. Drill a 1/4" hole down the middle of the plug to connect to the liner.
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Here is the breech plug in my rifle green mtn barrel 36 inch length (internal 351/2) but the touch hole is 1/4 x28 and is located just over 3/8 inch from the breech end of barrel. the plug is 1/2 and is filed to 3/8 on the touch hole side . The rifle has a date 1-91
1 is this safe ?
2 the builder has marked max load 100 3fff ?
3 can/should this be replace(and at what cost)?
(https://i.ibb.co/9ZwVz6k/DSC02968.jpg) (https://ibb.co/km39kjs)
I don't like it and would not have it - period.
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I'm looking for a replacement /suggestion. Trying to improve/repair a 1991 build.
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I'm looking for a replacement /suggestion. Trying to improve/repair a 1991 build.
As much as I hate long plug threads with a chamber that would fix this. Ignore the existing threads strength wise. Run the threads 3/4"+ up past the liner. Be sure there is 5/8" of clean threads. Make a new long plug. Install the new liner like Hugh CVA or Pedersoli, in the side of the plug threads. Drill a 1/4" hole down the middle of the plug to connect to the liner.
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I'm looking for a replacement /suggestion. Trying to improve/repair a 1991 build.
I know of people who set up their vent liners like this all the time. They notch the face of the plug, install a vent liner and go on with life. Not the way I would do it, but there you go.
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The reason I would never do this is not because is can not work. But because it is perceived as poor quality work. If an accident were to happen the maker will be blamed. People sue. It does not matter if the shooter was at fault. IF the crappy plug is found out, then then the maker looses the lawsuit.
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My hunting rifle is from a Dunlap early Lancaster kit. Chambers Siler lock. When I first put it together I had to notch the 5/8" breechplug (tri-corner file) to clear the drilled touch hole (C profile 54 cal) it was hit or miss fire no matter how clean I kept breech face/touch hole. I installed a weight lighting liner and it's probably the most reliable firing rifle I ever owned.
Dennis
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The reason I would never do this is not because is can not work. But because it is perceived as poor quality work. If an accident were to happen the maker will be blamed. People sue. It does not matter if the shooter was at fault. IF the crappy plug is found out, then then the maker looses the lawsuit.
I agree. But, I see this sort of thing on old guns all the time, as I'm sure you have too. I'm not saying it's right, but it was/is done commonly.
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Recurve: I have personally seen a breech fail with your exact configuration of liner and breech threads! The vent did not have enough threads engaged in the threaded portion of the barrel. It blew the lock clean off of the rifle and it bounced up against the building he was standing next to - 25yds. away! I repaired the breech by configuring a new and longer breech plug - 1" and threaded the barrel deeper to fit the new plug. Then made a new liner to go through both the barrel wall and the counter bored breech plug! I would not trust your set up at all as you have drawn it! Hugh Toenjes - 40 yrs. experience building front stuffers!
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For example look at Hoot Als Rifle Shop under tip& tricks , Installing a vent liner.
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Your pic shows the vent liner protruding into the barrel, if this is so then Yes I would have it repaired as described above....Ed
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The vent liner does not protrude into the barrel , I just made it stand out on drawing. took a little file work to get that right. Thanks
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For example look at Hoot Als Rifle Shop under tip& tricks , Installing a vent liner.
http://www.hootalrifleshop.org/install_flashliner.htm
A good internet example of how not to do something. Remember you loose a couple of threads at the bottom of the hole and a couple at the base of the plug. You need relief a cut because you can not thread perfectly to the end. At best your 1/2" long 5/8 x 18 TPI plug will give only 6 or 7 full intact threads.
Then AL cuts a notch? Yikes.
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Where the idea of three threads comes from is ungraded threaded rod, not graded capscrews and certainly does not apply to pressure vessels. Because of material yielding there is a certain consistency in the distribution of load applied to each thread. Studies of the physics have established that for a typical grade 8 nut with 75% engagement cold rolled threads the percentage of the load taken by consecutive threads are approximately 34%, 23%, 16%,11%,9%, 7% respectively from the clamped side to the runout side. For clamping applications, testing provides no increase in thread shear strength by having full-thread engagement (discounting 70% of lead male and female thread sections) length in excess of the screw diameter. For blind hole clamping standard practice is for tapped hole depth to be 1.5 times the nominal fastener diameter; this to allow for minimum of 1 full diameter with 100% thread engagement. Except in special applications any clamping connection have thread engagement less than 80% nominal diameter is substandard and unacceptable for engineering integrity.
Pressure vessels are completely different from fastener clamping applications and should not be in any manner confused or combined. In USA it falls under ASME B31.1/B31.3 piping code, Europe, India and others have their own codes according to standards for pressure vessels applied to straight and tapered threads but the commonality amongst all codes is that no less than 7 full-threads of engagement are acceptable. On pressure vessel threaded connections engineer must discount 100% of lead thread and standard practice is to gauge connections such that the finished assembly attains minimum of 7.5 full-thread engagement. Minimum applies to all connections whether blind, flange or compression ring, thread engagement minimums and pass-through on flange connections have been established based upon combination of materials testing and historical failure data. Disruption of thread engagement are via notch or secondary penetration reduces load rating by a minimum of 125% of the notch/penetration area.
HK
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Al Hoots breech plug "notched" is what I have on my 1991 rifle ,looks the same :o and this is why I started this thread :-[
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You machinist types give me a headache. :P
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I recommend you (Recurve) invest in "Machinery's Handbook" - no need to buy a current volume you can get an older edition which will have MANY pages of ALL the info you want to know about mechanical design, manufacturing, drafting, toolmaking, and machinist. I have edition #25 and paid less than $25 for it. In the section on "Fasteners" you will find your answer to your question. It depends on many factors as you will see when you start reading the section but here is a "GENERAL" guide and that is 1.5 X diameter of the male screw with 75% clean formed threads will give you max strength. Go buy the book ;)
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so it takes 15/16" thread length of a 5/8 dia. plug with 75% thread engagement to provide full strength ?.
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Ron: It is not just "full strength" but a measure of "tolerance" that is needed in breech plug threads. Today's BP is a little more refined and more powerful than several hundred yrs. ago and at "middle age" we have more "newbies", today, who start to shoot muzzle loaders than when you grew up learning the techniques from your father. So there needs to be more safety factors involved. Just saying, Hugh Toenjes
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oh I realize that Blacksmoke, the threads are defined by "class" which defines how the threads fit. what I was asking was "what does the 75 % define ?" ….it's class ?,.... or what ?. if class,....why wasn't the thread classification used instead of a being expressed in some percentage ?. ( I realize that thread "class" defines the percentage of contact ("fit") of engagement between internal and external threads, but using a "percentage" doesn't express what class the threads are. I assume a plug/barrel should be 3A and 3B...…(I've never seen it defined as a "percentage" before). that said, if so,...75% doesn't seem to be all that good a fit.
this brings to mind how "precious" the taps and screw plates were to the builders back then !.
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Seems to me that there are three different things being discussed here: The minimum length of threads necessary to avoid a dangerous gun; the length of threads that reaches maximum safety of the join, without considering other factors; and the length of threads necessary to ensure that the join is at least as strong as the barrel itself.
To the extent it the first question can be answered objectively, the best answer so far comes from HelmutKutz: 7/7.5 full threads of engagement is the standard minimum for pressure vessels.
The second has been answered Paul Berkuta: 1.5 times the diameter of the male screw.
The third was answered by John Cholin: The area of the engaged threads should equal or exceed the area of the cross-section of the barrel immediately in front of the breech plug face.
Now, I have a barrel that needs a new plug, and I have been doing some back-of-the-envelope calculations using it as an example. It is approximately 1.03 at the breech, .45 caliber, with 5/8x18 threads. At 18 threads per inch, .42 inches of full threads is necessary to meet Mr. Kutz's minimum. The area of the barrel cross-section is approximately .8496 square inches, so if I use John's formula and hypothesize .5 inches of thread I get approximately .87 square inches of thread, meaning that the threads are as strong as the barrel wall itself at approximately 1/2" of engagement (ignoring the difference between 8620 and 1018 steels, for the moment. Also, is this for tensile strength or shock impact?) I could go with 15/16" of threads, but that would mean counterboring and drilling the touch-hole through the threads, necessitating lengthening the threads yet again to compensate. It also means that the breechplug can't be removed without mucking up the touchhole, which is a safety issue in itself IMHO. And, in the end, it wouldn't add anything to safety of the gun as a whole.
1/2" of threads, unnotched, in both 5/18-18 and 3/4-16, at the very least meet the minimum standards for strength. In the case of the barrel I looked at above, it doesn't appear that adding to that length gives any practical benefit, and it is a pretty stout barrel wall, rather more than the average these days, I suspect. Now, I am aware that 1/2" of breechplug is NOT the same as 1/2" of full threads - the threads of commercial plugs tend to end ~1/8" before the tang, and there is some thread removed around the face of the plug. However, it does look to me like the usual plugs found these days aren't all that far removed from the optimal length, and 1/2" or a bit more of full threads, with no notch on the breechplug, seems like a very achievable goal without resorting to long counterbored plugs or making dramatic alterations to traditional architecture. With big bores and breechplugs larger than 3/4", that could change, of course.
Now, I wonder, what about the thread lengths on touch hole liners....
Edited to add: Double checked my math and the area of the barrel cross section is .878, not .8496, so 1/2" inch threads almost exactly matches it (I've been ignoring significant digits and using 3.14 for pi, so the exact relationship is uncertain, but the two figures are very close. Doesn't change the overall conclusion, though.
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Keep in mind on big bores , 10,11,12, you don't reach near the pressure. So , I would assume you're not going to need a plug that is 3/4" to 1" long.
Getz, Rice, Hoyt, FCI and all the other barrel Mfg's except Colerain seem comfortable with a 1/2" plug in all calibers. I'll go with what the major MFG's feel safe with. Of course they all use 12L14 too so I imagine hardly anybody here uses their barrels anyway.
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I have several friends that are engineers. They told me that 3 full threads is the maximum strength. That is full threads. Remember it takes many more times the pressure to blow the plug than it does to blow the barrel.
AND a patched ball moves forward easier than that tightly threaded plug
will move backward.
There have been cases in to not too distant past of cast plugs in production
muzzle loaders blowing because of extreme over tightening by people who
had not the vaguest idea as to what stresses were created by the assembly
process.They blew out and left the threaded part of the plug in the barrel
because a fracture occurred in the last thread because of people who had
no idea what they were making. Horrible injuries and lawsuits followed.
My grandfather who was born in 1873 told me of a cruel trick played on
a mentally challenged man. A group of local knuckleheads got a single
barreled muzzle loading shotgun that was poor quality and filled the barrel
half full of powder and a big load of birdshot and talked the guy into firing
it.According to grandpa,the plug did blow and the man was killed.I am
thinking the whole thing blew up like a pipe bomb.
I was told for years that "You can't blow up a gun with black powder".
DON'T BELIEVE it.
Bob Roller
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This is what I have(this is a very close to what is in my rifle)
(https://i.ibb.co/nCwbtR7/Breech-Plug-Coned.jpg) (https://imgbb.com/)
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This is what I have(this is a very close to what is in my rifle)
(https://i.ibb.co/nCwbtR7/Breech-Plug-Coned.jpg) (https://imgbb.com/)
So reading the above 2 pages, it seems that plug would be safe Without the notch,,,, but is Not Safe with the notch?
If that's the case, then the unmolested plug with 7 full threads is only marginally safe to begin with?
Really? If that's the case, these muzzle loaders should be blowing up practically every day! Not to mention the old original ones with nothing more than 3 course threads, with a notch filed in them..... that have somehow managed to exist this long....
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acknowledging the 1/2 minimum thread engagement length school of thought,....as long as the short side of the plug leaves at least a 1/2 inch of threads,.....the plug is safe......given class 3a&b threads are used.
it would be interesting to know how the plug threads of the original guns compare to modern classification.
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This is what I have(this is a very close to what is in my rifle)
(https://i.ibb.co/nCwbtR7/Breech-Plug-Coned.jpg) (https://imgbb.com/)
So reading the above 2 pages, it seems that plug would be safe Without the notch,,,, but is Not Safe with the notch?
If that's the case, then the unmolested plug with 7 full threads is only marginally safe to begin with?
Really? If that's the case, these muzzle loaders should be blowing up practically every day! Not to mention the old original ones with nothing more than 3 course threads, with a notch filed in them..... that have somehow managed to exist this long....
I don't see anything wrong with this plug, as long as the threads actually prevent powder gasses from escaping past the breech, into the stock. Looks fine to me- I had guessed at 8 threads.
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there's not much taken off that plug. that said the notch does eliminate the seal with the inside shoulder in the barrel. part of what constitutes a well built rifle is arranging lock, flash hole and barrel locations so that this doesn't need to be done. I realize it sometimes is impossible to avoid when using a pre carved stock.
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I don't want to give anybody a heart attack, but I would wrap some Teflon tape around that rascal and screw it in the barrel and go on with life with out a care in the world. I would rather it wasn't notched but it sure as $#*! isn't going to blow out and the Teflon tape will plug any leaks…. I doubt it will leak the way it is now.
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Recurve,
I would expect the breech plug shown in your photo to safely hand any reasonable, properly loaded blackpowder charge. I don't make breech plugs that way for a different reason.
Straight threads, which is what you have on that breech plug, do NOT seal - there is a small amount of free space between the threads that allows the threaded male part to be turned into the female part. The sealing comes from the flat surface of the breech plug face being pressed up against the ledge in the breech formed by the larger diameter breech plug hole meeting the smaller diameter bore. The threads function as an inclined plane to force a tight fit between those two flat surfaces and achieving a seal. When you notch the face the sealing effect is lost and gas can flow backwards along and between the threads. The gas includes the vapor of sulfuric acid which is corrosive. It is POSSIBLE, not guaranteed just possible, that this will lead to corrosion over time. This is not desirable. Hence, Mike would use a sealing means to seal up the space between the threads to prevent this corrosion mechanism. I would use Locktite 242 rather than Teflon tape but that's just what I prefer.
Best Regards,
JMC
John Cholin
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it is possible when cuttingthreads with a lathe, to make a very slight interference fit between inside and outside threads, so that the plug turns in under just a bit of tension all the way in. threads of this type will help seal the breech. high power gunsmiths (especially target gunsmiths) use this slight interference thread design when barreling modern actions to ensure no movement between barrel and action during the shot. it is actually tighter fitting than class 3A&B threads and requires ant-seize compound to be used or the threads will surely gall..
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it would be interesting to know how the plug threads of the original guns compare to modern classification.
I can shed a little light here as I've had a number of originals apart over the years. Basically, when screwing them in, you can screw them in by hand, and you'll only need a wrench for the last 1/4 to 1/2 of a turn. When unscrewing an original breech plug, you'll need a wrench to pop it loose, turn it maybe a half turn with a wrench, then unscrew it by hand. Most of these threads look more like a course thread modern pipe thread.
Most all of the guns I worked on were flint era and early percussion originals. As the guns get closer to the 1850's/60', the threaded fit of all the fasteners tighten up considerably.
That's not to say that there aren't exceptions to what I've said above, because I'm sure there are. That's not to say that some original gun didn't blow a breech plug at some point, but I've never seen an original gun that showed any signs of that, either as broken pieces or as repaired.
Just my 2 cent experience,
John
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Here is another picture of this style breeck plug taken from page 66 of the first edition of the Lyman Muzzleloaders Handbook.
(https://i.ibb.co/F0gB5gP/breech-plug.jpg) (https://ibb.co/qWkRNkZ)
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Remember, the first thread is to be discounted as non-load bearing, thus a minimum of nine full threads are required to achieve the minimum seven full threads of load bearing surface. Adding minimum necessary 125% safety factor increases minimum to 11.25 threads or 0.625" thread length.
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In the section on "Fasteners" you will find your answer to your question.
Fasteners are not calculated in the same manner as threaded pressure vessel fittings.
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This is what I have(this is a very close to what is in my rifle)
(https://i.ibb.co/nCwbtR7/Breech-Plug-Coned.jpg) (https://imgbb.com/)
So reading the above 2 pages, it seems that plug would be safe Without the notch,,,, but is Not Safe with the notch?
If that's the case, then the unmolested plug with 7 full threads is only marginally safe to begin with?
Really? If that's the case, these muzzle loaders should be blowing up practically every day! Not to mention the old original ones with nothing more than 3 course threads, with a notch filed in them..... that have somehow managed to exist this long....
Bare electrical wires are safe as well until someone touches them or something causes them to contact that which they should not. Steam boilers on locomotives were quite well designed though not properly inspected nor protected for corrosion. Just because one was fired a thousand times does not mean it will not explode on the 1001 firing. Safety factors have been developed mostly by learning from failures. As I responded to the other post, seven load-bearing threads are minimum whereby nine are required to achieve the seven load-bearing and on an 5/8"-18 plug an addition 2.25 threads are required to meet the absolute minimum safety factor, thus 11.25 threads total. Another 125% minimum must be added for any interruption in threads such as the notch or drilled hole as shown by another person.
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Helmut - are you referring to this style breech when referring to a drilled breech?
(https://i.ibb.co/GFBmtsq/H-Toenjes-breeching.jpg) (https://ibb.co/Pt3k9Td)
let my country awake (https://poetandpoem.com/analysis-mind-without-fear-rabindranath-tagore)
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I have been hesitant to get back into this one. Here goes....
I would never own a gun so breached. I would never do it that way, it is as easy to do it right as to do it wrong after-all. I would never buy a gun so breached. I check plugs before I use a barrel. IF somebody sold me such a gun I would demand a refund. Under no circumstance would I shoot it.
I am opinionated. That is based on 50 years around guns and 30 years as a forensic scientist specializing in firearms matters.
Catching a plug in the face is pretty serious, you will probably die. There is no good reason to do such sloppy work. If it ,"came out wrong" then start over and do it right.
Antique guns have no sway with me. We know better now, so do it right.
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Helmut - are you referring to this style breech when referring to a drilled breech?
(https://i.ibb.co/GFBmtsq/H-Toenjes-breeching.jpg) (https://ibb.co/Pt3k9Td)
let my country awake (https://poetandpoem.com/analysis-mind-without-fear-rabindranath-tagore)
Shown in the picture are eight load bearing threads which itself is insufficient for a 5/8"-18 plug as explained previously, such requires a minimum of 11.25 threads. Perhaps drawing is not to scale but it appears to be fairly accurate considering the 0.440" liner center measure.
The area of the interruption, this case being 0.3125" diameter touch hole liner, is no longer load bearing and must be accounted for at 125% compensation factor.
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Looks like we're working up to Mikes' 12 inch long breech plug again ;)
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some pics of original breech plugs for your viewing pleasure StevenV
(https://i.ibb.co/Mh6d53w/IMG-4419.jpg) (https://ibb.co/7z4hN6M)
(https://i.ibb.co/rxkCtDr/IMG-4421.jpg) (https://ibb.co/CbBktRG)
(https://i.ibb.co/c8GZN09/IMG-4423.jpg) (https://ibb.co/ykwZ8tC)
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breech plug for current build StevenV
(https://i.ibb.co/X2g1djz/IMG-4461.jpg) (https://ibb.co/smGnDbF)
(https://i.ibb.co/L6rqCMR/IMG-4462.jpg) (https://ibb.co/gwdXDG9)
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It is interesting that some are calculating what sort of threaded length is required to ensure the breechplug’s hold on the barrel is no more likely to fail than the barrel itself, and using that as a standard. That clearly is a new standard not previously employed in making muzzleloading, black powder-burning barrels. Has something changed?
A good many of the originals pictured here have been shot a lot. Some were likely in service for a hundred years. Having disassembled a decent number of drum and nipple percussion rifles, the majority have the drum set into the front of the breechplug with relief of part of the threaded portion. The drum must be removed before the breechplug.
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I'll tell y'all (practicing my southern speak for the Knoxville show ;D) a little story of a gun that came across my bench 20 or more years ago. It was a blowed up TVLLE made by Allegany (I think). The owner was drunk and felt threatened by hostiles on snowmobiles whilst camping in the dead of winter in a Tee Pee. So he grabs his gun and horn and dumps who knows how much powder down the barrel straight from the horn (like in the movies ::)) and plops a ball on top. Staggers outside and takes a pot shot at said scary hostiles. TVLLE promptly comes apart. Vent liner exits barrel taking lock and lock screws plus sideplate plus much wood with it. TVLLE is now laying on the ground in many pieces and Mr. Drunk says " Golly, my gun broke!" Or something to that effect.
So anyway, the TVLLE parts end up on my bench sometime later to get a quote on a possible restock. "Not likely" says I. Main reason is I don't want this guy owning one of my guns an me facing a law suit some day because of a repeat situation. Secondly, the barrel appeared to be completely unharmed except it didn't have a vent liner in it anymore. But, I wondered about the stress of being blowed up and it's possible effects on the barrels future.
So, a catastophic failure and the breech plug held in there on a 20 bore with a massive overload. I don't recall if it was a 1/2" or 5/8" long plug, but I'm not sure if that makes a difference in this case. Oh, 12L14 barrel too.
Next scenario: This happened to me. 1" X .50 Douglas barrel. 80gr 3f. Loaded powder,patch ball, rammed home. Then was distracted and again loaded powder and short started the ball and was distracted again before I could ram it home, I was then called to the line as it as my turn to shoot. I pulled the trigger. Catastophic failure. Gun shatters . Top flat disapears for ever. 5/8" long Breech plug is still in the stock.
Next scenario: A customer loans his neighbor his high end flint pistol I built for him several years before. It is to be used as a New Years Eve party noise maker ::). Said pistol is Sterling mounted and has yards or silver wire in it. I wasn't there so I can't say what exactly happened but I suspect the booms weren't loud enough so increasing amounts of powder were drunkenly added trying to achieve the ultimate boom. High end wired pistol stock finally shatters. Barrel and plug stay intact. (.50 smoothbore 1/2" long plug, 12L14) Everyone is highly disappointed. Pistol ends up on my bench for a "please fix now" ???. This was 15 or 20 years ago. The shattered pistol stays in a drawer, now and forever. You blow up a gun of mine like that, you don't get it back.
My conclusion: The barrel or vent liner will fail before the plug blows out. Of course it's nice if everyone loads their gun properly so we don't have to worry about how it may or may not come apart. I know I pay alot more attention while I load and always run my rod down the bore when I get to the line to shoot just to make sure I have loaded properly even though I know I did.
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It is interesting that some are calculating what sort of threaded length is required to ensure the breechplug’s hold on the barrel is no more likely to fail than the barrel itself, and using that as a standard. That clearly is a new standard not previously employed in making muzzleloading, black powder-burning barrels. Has something changed?
A good many of the originals pictured here have been shot a lot. Some were likely in service for a hundred years. Having disassembled a decent number of drum and nipple percussion rifles, the majority have the drum set into the front of the breechplug with relief of part of the threaded portion. The drum must be removed before the breechplug.
Again I say is the locomotive steam boiler that explodes on the 1001 firing still considered "safe" because it didn't explode on the 1000 previous firings?
Safety measures are derived primarily from examining previous failures and the engineering minimums for pressure vessels are different not. But for sake of argument what point is there in showing only those which have not failed when there is no means to show those which have failed? If there were basis in engineering to support fewer course threads, why then have we standards for multiple finer threads in all modern applications? How does one argue against the NPT standardization whereby the minimum number of load-bearing threads ranges from 7.13 to 12.1 respectively for nominal sizes 1/8"-6" and further wonder is why 8tpi on a 6" diameter pipe and not say course thread of 3tpi based on argument here?
The question asked is, "What's the minimum safe breach plug?" to which the answers are given relative to the accepted engineering data which has been derived over centuries of application. I just wish you to provide basis for the argument of few course thread originals when you are not using that in modern application. Sorry but this is like arguing for modern steam boilers to be assembled with wrought iron rivets rather than modern arc welding because we see that some have managed to survive while ignoring all those that have exploded. If I misunderstand, please explain because I am at a loss to understand why there is such argument against engineering based logic.
HK
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TKS Helmut, for answering my question.
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It is interesting that some are calculating what sort of threaded length is required to ensure the breechplug’s hold on the barrel is no more likely to fail than the barrel itself, and using that as a standard. That clearly is a new standard not previously employed in making muzzleloading, black powder-burning barrels. Has something changed?
My thinking is that the explosion is contained by the barrel assembly as a whole, not just the breechplug threads, and the assembly is only as strong as its weakest point. Since the strength barrel walls are a fixed point, I figure that any breechplug that is as strong as the barrel walls is as safe as it can get - If you have two identical barrels, one breeched with threads that will fail at 55k psi and one that will fail at 100k psi, the 100k breech is no safer than the weaker one if the barrels themselves will come apart at 50k psi.
I don't particularly like the idea the of making a breech that cannot be taken apart to check for corrosion, remove a stuck ball or cleaning jag, de-hex it after missing a shot at a wolf :o, etc. That isn't a theoretical concern, either - on my to-do list is disassembling and examining a percussion rifle with a interlocking plug and drum system that hasn't been used or cleaned since it was used to shoot some pyrodex blank loads and cleaned by an unsupervised teenager about fifteen years ago. It is hard enough with a percussion system - I have no idea how I would do it with a flint setup with no way to unscrew the liner. While I don't want to compromise on strength, getting fixated one point and overengineering the breech threads at the expense of other concerns seems like a bad idea.
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Given that there must be at least hundreds of thousands of shots made each year with muzzle loaders, let's see some pictures of blown breech plugs.
One's blown with smokeless powder or dynamite don't count!
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If I misunderstand, please explain because I am at a loss to understand why there is such argument against engineering based logic.
HK
Helmut, I don't think that more than a handful of guns made, both today and in the past, that meet those standards. Even if the breechplugs meet them, I suspect quite a number of nipples, drums, and vent liners do not have enough threads. I don't believe that there are any components off the shelf that can be made to work - Even Green Mountain barrels only have about 5/8" of threads in them, and the plugs available have about a 1/8" gap at the end between the threads and the tang area, which means that about 1/2" is the max one can get without reworking the barrel breech or making a plug from scratch. For those of us without access to a lathe or the skill do use one, that means sending EVERY barrel out to be reworked. That complicates things a mite.
At the same time, there just doesn't seem to be much evidence that plugs fail, unless they are very poorly installed (nobody is seriously arguing that plugs are OK with just three threads - most plugs, notched or otherwise, seem to have around five or six). Given that these figures also have weight of several hundred years of trial and error, I can see why some people might be a bit skeptical.
I do appreciate you sharing your knowledge with us, and I'm sure that there are others here as well. I'm certainly not ignoring it.
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Here is the breech plug in my rifle green mtn barrel 36 inch length (internal 351/2) but the touch hole is 1/4 x28 and is located just over 3/8 inch from the breech end of barrel. the plug is 1/2 and is filed to 3/8 on the touch hole side . The rifle has a date 1-91
1 is this safe ?
2 the builder has marked max load 100 3fff ?
3 can/should this be replace(and at what cost)?
(https://i.ibb.co/9ZwVz6k/DSC02968.jpg) (https://ibb.co/km39kjs)
Leaks gas and fouling into the threads. I never do this.
Dan
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It is interesting that some are calculating what sort of threaded length is required to ensure the breechplug’s hold on the barrel is no more likely to fail than the barrel itself, and using that as a standard. That clearly is a new standard not previously employed in making muzzleloading, black powder-burning barrels. Has something changed?
My thinking is that the explosion is contained by the barrel assembly as a whole, not just the breechplug threads, and the assembly is only as strong as its weakest point. Since the strength barrel walls are a fixed point, I figure that any breechplug that is as strong as the barrel walls is as safe as it can get - If you have two identical barrels, one breeched with threads that will fail at 55k psi and one that will fail at 100k psi, the 100k breech is no safer than the weaker one if the barrels themselves will come apart at 50k psi.
I don't particularly like the idea the of making a breech that cannot be taken apart to check for corrosion, remove a stuck ball or cleaning jag, de-hex it after missing a shot at a wolf :o, etc. That isn't a theoretical concern, either - on my to-do list is disassembling and examining a percussion rifle with a interlocking plug and drum system that hasn't been used or cleaned since it was used to shoot some pyrodex blank loads and cleaned by an unsupervised teenager about fifteen years ago. It is hard enough with a percussion system - I have no idea how I would do it with a flint setup with no way to unscrew the liner. While I don't want to compromise on strength, getting fixated one point and overengineering the breech threads at the expense of other concerns seems like a bad idea.
If it was not cleaned after shooting pyrodex, even for a few days I would not worry about looking at it. Its no longer usable so just plan on replacing it.
I NEVER remove a liner. I learned this LONG ago. Like 40 years ago. If its put together right there is no need. Seating the liner against a shoulder means there is no need and I sure don't want one with a screw driver slot. Not only is it ugly its not needed. Shouldering the liner drastically reduces the pressure on the part making it even safer. Unfortunately most of the store bought liners don't allow this.
Dan
Dan
(https://i.ibb.co/bsKg51B/UNADJUSTEDNONRAW-thumb-38d9.jpg) (https://ibb.co/QPKFv9N)
(https://i.ibb.co/VNQFp3H/UNADJUSTEDNONRAW-thumb-38db.jpg) (https://ibb.co/26szY58)
(https://i.ibb.co/k4763Gh/UNADJUSTEDNONRAW-thumb-38dd.jpg) (https://ibb.co/m9jFvRH)
(https://i.ibb.co/VLpnhDG/UNADJUSTEDNONRAW-thumb-38e1.jpg) (https://ibb.co/qDFq498)
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Photo sucks but it shows the breech seated and shows where the vent enters the "cup". The liner is shouldered.
(https://i.ibb.co/J3M6MFL/q-M97mzz-NToq-C7oav-Jy4-M1w-thumb-3b25.jpg) (https://ibb.co/tLWjWPf)
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This is a barrel maker installed breech, no seal at all and lost of fouling in the fouling trap thus created. The plug threads can be seen if you look past the reduced diameter "face" of the plug. I replaced the barrel for the guy since it also had deep dovetails in the waste and since it had been in my shop I did not want to be responsible.
Dan
(https://i.ibb.co/nBn0yx0/UNADJUSTEDNONRAW-thumb-46db.jpg) (https://ibb.co/tzxh6Vh)
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It looked like this after I pulled it. Before and after removing the trapped fouling. There is no excuse for this. Its a commercial barrel maker but they were producing hobby home crapsmanship. Maybe still are. This is why I never use a barrel breeched by someone else unless its pulled and checked. Tome ordering a breeched barrel is a waste of time. Had it been a percussion and shot with corrosive "replica" powder the breech probably would have been rusted in.
Dan
(https://i.ibb.co/Tg79P69/UNADJUSTEDNONRAW-thumb-3a89.jpg) (https://ibb.co/yQZHgtH)
(https://i.ibb.co/FxRxkBW/UNADJUSTEDNONRAW-thumb-3a9b.jpg) (https://ibb.co/yfHfm8R)
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If it was not cleaned after shooting pyrodex, even for a few days I would not worry about looking at it. Its no longer usable so just plan on replacing it.
I NEVER remove a liner. I learned this LONG ago. Like 40 years ago. If its put together right there is no need. Seating the liner against a shoulder means there is no need and I sure don't want one with a screw driver slot. Not only is it ugly its not needed. Shouldering the liner drastically reduces the pressure on the part making it even safer. Unfortunately most of the store bought liners don't allow this.
Dan
I wasn't clear enough, I guess. The teenager in question was my younger brother, back in the day. I'm sure he cleaned it, I'm just not sure how well, since I was off at college at the time and not around to supervise him, and it has been sitting around in a closet since then.
I was talking about trying to disassemble a long, counterbored breech in which the liner is inserted through the breech threads to reach the powder chamber, such as in the diagram Blacksmoke posted. I'd have to remove the vent liner to unscrew the breech in that scenario.
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(https://i.ibb.co/FxRxkBW/UNADJUSTEDNONRAW-thumb-3a9b.jpg) (https://ibb.co/yfHfm8R)
[/quote]
If you run the tap drill into the plug like the photo above, it will not be supported on one side and will then make an oblong hole. When the hole is tapped for the liner you will only get a partial thread. A fine thread like 1/4x32 makes it worse. This increases the likelihood the liner will be blown out.
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(https://i.ibb.co/FxRxkBW/UNADJUSTEDNONRAW-thumb-3a9b.jpg) (https://ibb.co/yfHfm8R)
If you run the tap drill into the plug like the photo above, it will not be supported on one side and will then make an oblong hole. When the hole is tapped for the liner you will only get a partial thread. A fine thread like 1/4x32 makes it worse. This increases the likelihood the liner will be blown out.
[/quote]
No, the vent liner will be supported on all sides by the barrel. The vent liner will stop at the point it enters the bore.
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what i'm gathering here is that in most cases, the lock panels of stocks ae actually too far back on the stock, or the barrel channels aren't being opened up far enough back by the builders to position the vent holes where they should be placed on the barrel. I assume these photos are associated with barrels used on pre-carved stocks, anyways. if the former is trye,...why is it that the pre-carved stock suppliers don't reposition the lock panels and barrel channel ends to accommodate correctly installed vent holes.
I guess this is one good reason to start from a blank, given the builde understands the proper layout needed.
maybe there's a need for a precarved stock that has just the butt stock and the beginning of the grip area shaped up, with the lock panel area left as a plank and the forend just left square. it would still save some time and would accommodate getting the lock panel flash hole layout association correct.
then, a builder could get the barrel/plug/ flash hole in the right position first, before the lock panel is let in.
I understand that a lot of this is the small details that separates schools of design, but building a correctly functioning gun with it's components in the correct locations with safe construction, is far more important than accomplishing any accuracy in copying some architectural school.
just my opinion,.....does this make sense ?. i would much rather see a suggestion of any particular school be only a suggestion because i built the gun with it's parts in the correct relationship.
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I was not clear....After you drill through the barrel and hit the plug, you are now making an interrupted cut. The drill bit will then put a side load on the muzzle side of the hole in the barrel. It will then continue to cut the hole in the barrel and make it oblong to some degree.
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that is correct, and the reason is because of the location of the lock panel on the stock. …..in order to get the cock to strike the nipple or the frizzen correctly, the lock has to be in a specific location. when that location isn't coordinated with the location of the flash hole in the barrel, parts start getting moved around and putting a divot in the face of the plug is the usual remedy. if the lock panel on the stock is in a better location, the plug can be installed without interrupting it's threads and the liner hole can be drilled without the drill bit hitting the face of the plug,...as it should be done.
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Pre-carves/ pre-inletted can be more trouble than they are worth. Sometimes time I spend scratching my head on how to work around what is there is more than if I just started from a plank. I would definitely determine if the lock inlet is correct before I cut on it. Send it back if it is wrong. Better yet, get the stock with no lock inlet.
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Originals were not built from precarved stocks yet most drum percussion guns have the drum going into the front edge of the breech plug.
I hypothesize that builders back then really wanted ignition to happen at the rear of the powder charge, and in their experience building and repairing guns, somewhere between 3/8”and 1/2” of threads was just right.
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I have read that the builders were somewhat anal about that. still,...it would seem to me that it isn't all that hard to get the flash hole in the right place. a few simple measurements is all it takes one the plug is fit. I see no reason to drill a flash hole anywhere before I know i've got the plug well fit. to me, it's just back-a$$wards to do it any other way and if the lock panels, or lock inlet, or barrel channel isn't right, the stock should go back to the supplier. or be corrected if it can, before it leads to having to grind on the plug face.
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On many kits the barrel has to be moved back 1/4" or more to get the touch hole to line up to what we consider "the correct position". Most newbies don't realize this or some folks are just too lazy to back them up that far.
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UH-OH. Just had another thought about possible disaster. What about vent liners? If they don't shut off against a shoulder like breech plugs do won't gases and crud creep up the threads and rot the threads out until the vent liner blows out? Seems a sure thing, even with the way Hugh and Jerry put there liners in chambered breeches.
I'm so paranoid now I think I'll give this up and start quilting with my wife. Wait, she uses sharp needles. I could stab my self and bleed to death. ;)
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No, Mike, it’s different when the hole is threaded from the side. Just kidding! I think vent liners are just as controversial as breechplugs. I guess it’s the shoulder at the surface of the barrel that is the clincher?
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If I misunderstand, please explain because I am at a loss to understand why there is such argument against engineering based logic.
HK
Helmut, I don't think that more than a handful of guns made, both today and in the past, that meet those standards. Even if the breechplugs meet them, I suspect quite a number of nipples, drums, and vent liners do not have enough threads. I don't believe that there are any components off the shelf that can be made to work - Even Green Mountain barrels only have about 5/8" of threads in them, and the plugs available have about a 1/8" gap at the end between the threads and the tang area, which means that about 1/2" is the max one can get without reworking the barrel breech or making a plug from scratch. For those of us without access to a lathe or the skill do use one, that means sending EVERY barrel out to be reworked. That complicates things a mite.
At the same time, there just doesn't seem to be much evidence that plugs fail, unless they are very poorly installed (nobody is seriously arguing that plugs are OK with just three threads - most plugs, notched or otherwise, seem to have around five or six). Given that these figures also have weight of several hundred years of trial and error, I can see why some people might be a bit skeptical.
I do appreciate you sharing your knowledge with us, and I'm sure that there are others here as well. I'm certainly not ignoring it.
I still beg for an answer as to why anyone would argue against the proven data when it's not beyond reason to create acceptable designs. Certainly we are limited no longer by available technology tooling, yet there is certainly an underlying insistence in accepting some while rejecting others.
I previously asked why heavy course threads are held up as comparison to modern fine threads when the load bearing and stress factors are completely different and can easily be modeled by FEA (Finite Element Analysis) software or even destructive testing if one wishes to observe the physical specimens.
One said something about the force being less on the plug than the barrel which is not correct as all pressure is equal at any given point and the force applied via flow dynamics in response to rapid pressure or flow changes such as those we observe when combustion is contained within a pressure vessel as being discussed here. Furthermore, the same rapid pressure changes and flow dynamics also affect every other parts of the assembly like vent liners in unique ways.
In design engineering there is no acceptable failure rate, thus we design things with a certain amount of safety factor so as to eliminate the chance of failure under the acceptable use conditions. My greatest concern here are those who make arguments which seemingly assume some acceptable failure rate based solely upon the lack of data. To me this is like attempting to prove a negative.
HK
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Helmut, I believe your questions have been answered by real world proof. Barring human error, I.E. stupidity or distraction in loading, 1/2" long breech plugs, regardless of their diameter, are not blowing out, knotched breech plugs are not blowing out, and 12L14 steel barrels are not blowing apart. Zero failure rate is unachievable as long as there is a human element involved, even properly built and maintained steam boilers have blown up due to human error. For azero failure rate we would probably need the 12" long breech plug Mike mentioned along with a 3" wall thickness on a .45 caliber barrel in case someone loaded it improperly.
Mark Poley
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rot the threads out until the vent liner blows out?
Lest we forget, most vent liners are retained in the barrel by the lock bolster making it near impossible to blow the liner out. Also, by the time the threads are rotted out, the touch hole is likely so big that it relieves any pressure build up.
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One saving grace for liners - and drums for that matter. The smaller the threaded diameter, the lower the actual pressure in psi. By thee same token, the larger the diameter, the higher the pressure.
There is more pressure against the threads of a 3/4" breech, than a 3/8" breech.
Crappy machining is why drums blow out, now and then - not enough threads?
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rot the threads out until the vent liner blows out?
Lest we forget, most vent liners are retained in the barrel by the lock bolster making it near impossible to blow the liner out. Also, by the time the threads are rotted out, the touch hole is likely so big that it relieves any pressure build up.
Read my previous post. I have seen a blown out vent liner. Took the lock, screws and sideplate with it shattering the stock
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Fool proof is largely determined by the size of the fool. I have removed breech plugs from original barrels 150 years old that had no seat whatsoever. The barrels were no longer safe to shoot in my opinion but the plugs were as good as when installed and took a great amount of force to remove. The threads were a force fit and rounded. The touch holes or percussion hole went through the plugs with no liners.