How much of a problem is a breech with threads exposed to combustion?

[Jerry V Lape]

How much of a problem have you had cleaning a breech where the threads are exposed?  Were the originals all built with the breech plug mating up with the shoulder of the rifled portion of the barrel?  Or a contemporary rifle where the touch hole cuts into the edge of the breech plug as can happen with a touch hole liner for example? Asking about actual experience with this, I understand the theoretical preference. 

[Dan Fruth]

I went to school with Jack Haugh's children, and built my first gun in his shop in Plymouth Ohio. He always placed the back of the pan even with the breech of the barrel, and the vent hole went into the threads. We filed a lengthways Vee exiting at the face of the breech, nicely radiused. I never had any problems with this method, and as far as I know he continued to build this way. My experience...not conjecture.

[jerrywh]

  I have never seen an original barrel of even a gun made in the mid 1800s that had a breech plug seated against a shoulder in the back of the barrel. They were all just a forced fit or very tight thread sealed. Most of them had a recess cut out of the front of the plug where the touch hole entered that looked like it was done with a round file. Some of the guns I looked at were way over 200 years old and showed very little signs of corrosion.  The one exception was African trade gun that looked like it had never been cleaned. I still have some of the plugs in my shop. This shoulder thing is pretty recent. I never heard of it until about 20 years ago. It is a good idea but in my opinion Not necessary. Question-- Where will your gun be in 2217.  Do you think it have a corroded breech plug? If it is sealed it won't, if it even exists. Wrought iron corrodes much faster than mild steel. Go figure. As for mine, most of them are shoulder sealed because I bought my barrels.

[davec2]

I built my very first gun in 1969.  I was a sophomore in high school and bought one of the Dixie Gunworks .45 cal barrels.  I made the lock and all.  The architecture is $#@* because all I had to go by was a 2 inch black and white photo of what a rifle should look like in the Dixie catalog.  I shot the gun for many, many years.  About two years ago, I decided to pull the breech and look at the barrel condition.  After all the comments I had read about double seating at the end of the barrel and on the shoulder, I was very surprised to see that to prepare the breech, they had just run a 1/2-20 tap into a .45 caliber bore.  No shoulder....no nothing......and NO degradation or corrosion....after some 40 years of shooting and cleaning. 

I wouldn't worry too much about a perfect shoulder.

[Scota4570]

Long ago I did a 12 ga with a tapered pipe thread.  Seemed to work OK.  I don't see why it would be a problem if the threads were tight.  It would seal just fine, especailly if you used teflon dope or tape. 

[Bob Roller]

Long ago I did a 12 ga with a tapered pipe thread.  Seemed to work OK.  I don't see why it would be a problem if the threads were tight.  It would seal just fine, especailly if you used teflon dope or tape.

I have unbreeched a few relics with what appeared to be a pipe thread.
The idea and theory is that the ball/shot load or whatever will move forward easier
than the breech plug will move to the rear.Breech plugs that are so tight that
special tools are required to remove them are not needed and can add one more
level of irritation if they must be removed.

Bob Roller

[Eric Krewson]

The breech fit on my first gun was pitiful, I even notched the plug face because I drilled the touch hole in the wrong place. On my final assembly I put so much anti seize compound on the plug threads I had to wipe it off the plug face after I got the plug in. I am pretty sure I pulled the plug for some reason a few years later and found everything pristine in spite of my lousy fit.

[rfd]

i find notched/trough flat face breech plugs are annoying for cleaning out and can cause ignition issues, particularly if you don't wanna deal with between shot fouling control.  i want a FLAT plug face and i don't care that the touch hole will be located somewhat past that flat face.  and i want that plug well Nikal greased, too.  here's one that's giving me ignition fits due to bp residue accumulation, and i've got to open up and smooth that trough, or maybe i'll dish it with a ball cutter ...

[n stephenson]

I`ve got 5or 6 old wrought iron barrels and sections , and a couple of old plugs. Non of the bores appear to have any shoulder. The threads are very coarse and only one plug is close to 1/2 inch long the other 2 are closer to 7/ 16. Non of these were blown out or up and don`t show excessive corrosion . The bores are in much worse shape than threads or plugs. I think that people worry much more about things like that now than they did back then . They just plugged the barrel and moved on to the next step.  JMHO  Nate

[P.W.Berkuta]

AH -- the pendulum is swinging now in the opposite direction . Not too long ago it was stated that you MUST fit a breach plug with it contacting both front & rear of the breach plug to barrel . I guess the trend now will be to just screw the breach plug in till it stops anywhere it want .

[jerrywh]

AH -- the pendulum is swinging now in the opposite direction . Not too long ago it was stated that you MUST fit a breach plug with it contacting both front & rear of the breach plug to barrel . I guess the trend now will be to just screw the breach plug in till it stops anywhere it want .

   Not so. It must be tight and sealed. Most of the old plugs I pulled has a concave surface. The main strength of a breech plug is the fact that the surface area of the face is so much smaller than the surface area of the combustion chamber. According to my calculations most breech plugs would require about 4 time the pressure to blow out than it would take to blow a barrel at the chamber. However I am not an engineer and do not know how to figure such formulas as hoop strength. Dave Crisalli is a expert a  this sort of thing. I have four good friends that are Engineers who I depend on for such information. I don't just guess.

[davec2]

RFD,

Here is a tool I made to hold a breech plug in the lathe or mill for shortening, cutting back the shoulder, etc.  On this breech plug I did exactly what you said and cupped it out in the lathe with a ball end mill, then polished the surface so it cleans very easily.  I have also done this and then put in a touch hole liner that intersects the edge of the plug.  The only thing I have to remember then is that if I ever want to remove the breech plug, the touch hole liner has to come out first.

[rich pierce]

One has to work to current standards or better if selling rifles. I unbreech my guns every couple years for inspection.  They all look great. But I don't shoot that much.

Now that barrels ARE threaded with a shoulder as opposed to a sort of pipe thread setup i feel it is important to have goof breechplug contact with the shoulder. Because with the shoulder, there's an opportunity for moisture and fouling to eat away in any gap present.

That gap can't exist if there is not a shoulder, so comparing how they did it then versus now seems like apples and oranges to me. 

[P.W.Berkuta]

AH -- the pendulum is swinging now in the opposite direction . Not too long ago it was stated that you MUST fit a breach plug with it contacting both front & rear of the breach plug to barrel . I guess the trend now will be to just screw the breach plug in till it stops anywhere it want .

You do all notice the emojis don't you --- this comment is "tongue in cheek" 

[Cory Joe Stewart]

AH -- the pendulum is swinging now in the opposite direction . Not too long ago it was stated that you MUST fit a breach plug with it contacting both front & rear of the breach plug to barrel . I guess the trend now will be to just screw the breach plug in till it stops anywhere it want .

You do all notice the emojis don't you --- this comment is "tongue in cheek" 

Despite being tongue in cheek there is still a point made here.

[n stephenson]

Rich, You are correct . With the shoulder that is now used , I agree , you don`t want a gap for moisture and fouling build up. My point about the originals was that, those guys weren't machinists ,they were 18th century barrel makers and, what they did WORKED. I`m sure someone will comment that they weren't facing litigation if they failed which, may be true. But I`m sure that if they were having breech failures they wouldn't be in business long ,or perhaps been thrown out of a guild . Much of the parts that we have today ,came about during the revival period of muzzleloading , and we are blessed to have them available. But a lot of it was approached by modern machinists with modern machinist training and mindset which, in some cases was good ,but other things got over engineered,  ie. deeper threaded breechplugs which threw the lock alignment out for certain rifles . The old smiths and gunstockers  had to be efficient and they did have everything to lose if they messed up too.   Maybe they didn't shoulder them as much as today because they didn't have to.

[davec2]

Despite my own experience with the Dixie barrel more than 4 decades ago, I do try to make any current breech plugs bottom on the correct flat and on a shoulder.  I think it prudent.  However, I don't stress about it much if it cannot be done perfectly on a particular build or if there is some small discrepancy or other.  Good engineering practice is to design hardware that does NOT bottom in two separate places as this is particularly hard to achieve in many cases.  In our situation, we usually bottom on the top barrel flat and actually yield material on the face of the plug and at the shoulder by torquing the daylights out of the plug.....also not good engineering practice. 

I had this conversation long ago with Don Getz about over torquing a breech plug.  The considerable force exerted on the threads actually weakens the plug's ability to resist the pressure in the breech when the gun is fired.  I have lubricated a Grade 8, 3/4 inch bolt with STP and then demonstrated that I could strip the threads out of a Grade 5 nut with a standard open end wrench.  If you have to put so much torque on a breech plug that you start to yield the threads, you are not very far from failing the threads.....and that's with the barrel lying on the bench with no internal pressure.

Bottom line, do a good job fitting the plug and not leaving a gap that is hard to clean....but don't go crazy about it all.  The gun will work just fine anyway and very likely outlast anyone reading this thread.

[Mike Brooks]

BLASPHEMERS! 

A personal  observation.... In some calibers a  "shoulder" isn't possible. It seems the bore is just threaded to except the breech plug and that is it, oddly, this seems to be the same practice as the old days. I spent considerable time with Don Getz and he wasn't overly concerned with this sort of thing.
 Personally I don't care if the breech plug threads have a shoulder or not. If there is a shoulder there the plug probably ought to snug up to it. If the threads are bore size than I don't worry about it.

The old stuff I have had apart was course threaded, plugs usually 3/8" long or a bit more and no shoulder to bump up against.

One of my pet peeves are breechplugs installed by gorillas. There is no reason to have to use 3' of cheater pipe on a wrench to turn a plug out, really earks my ernie.....

[bgf]

Despite my own experience with the Dixie barrel more than 4 decades ago, I do try to make any current breech plugs bottom on the correct flat and on a shoulder.  I think it prudent.  However, I don't stress about it much if it cannot be done perfectly on a particular build or if there is some small discrepancy or other.  Good engineering practice is to design hardware that does NOT bottom in two separate places as this is particularly hard to achieve in many cases.  In our situation, we usually bottom on the top barrel flat and actually yield material on the face of the plug and at the shoulder by torquing the daylights out of the plug.....also not good engineering practice. 

I had this conversation long ago with Don Getz about over torquing a breech plug.  The considerable force exerted on the threads actually weakens the plug's ability to resist the pressure in the breech when the gun is fired.  I have lubricated a Grade 8, 3/4 inch bolt with STP and then demonstrated that I could strip the threads out of a Grade 5 nut with a standard open end wrench.  If you have to put so much torque on a breech plug that you start to yield the threads, you are not very far from failing the threads.....and that's with the barrel lying on the bench with no internal pressure.

Bottom line, do a good job fitting the plug and not leaving a gap that is hard to clean....but don't go crazy about it all.  The gun will work just fine anyway and very likely outlast anyone reading this thread.

This is about where I try to be.  Wrenches/vises only stressed for last flat or less and not using my 250# body hanging off a 4 foot extension, just arm snug with a 12 or 14 inch wrench.  Decent contact  with shoulder.  If the threads are stressed to the max before combustion, as you say, they are too close to point of failure during combustion!

Not to open another can of worms, but the breeches I've seen appear to be 12L14, any idea how that compares with grade 8 in thread strength?

[Mike Brooks]

All/most custom barrel makers make their plugs out of what ever stock the barrels are made from. I graduated from grade 8....grade 12 too.

[davec2]

bgf,

12L14 yield strength = ~ 60,200 psi

Grade 8 bolt yield strength = ~ 130,000 psi

Note:  A grade 8 bolt in a 12L14 female thread doesn't buy you anything   

[bgf]

Mike,

That is what I figured, but wanted to confirm, not trying to troll on 12L14 . 

Dave,
Thanks for the numbers.  I wasn't going to suggest grade 8 plugs !  I just figured the thread strength of 12l14 was less than grade 8 bolt.  Actually, even grade 5 is 92k, it looks like.  So if you stripped the grade 5 nut, you had at least 92k, which is 50% beyond 12l14 failure, right?  This just makes me feel a lot better about not applying extreme torque to my breech plugs!

[flehto]

This discussion mentions the relative strengths of different  steels used for breechplugs and even though the "lowly"  12L14 steel is mainly used, don't hear of the breechplug blowing out when a bbl is burst.

W/ the modern practice of sealing the plug against a shoulder, only the resultant force of the  pressure times the bore dia is exerted on the breechplug and seeing BP pressures are low to moderate, the force exerted is low and nowhere near that req'd to strip the threads......Fred 

[Dan Fruth]

All/most custom barrel makers make their plugs out of what ever stock the barrels are made from. I graduated from grade 8....grade 12 too.

If you ask the barrel makers, you will find that most Buy their plugs from a company in the southern states already made, for a fraction of the cost to make onesy/twosey...