AmericanLongRifles Forums
General discussion => Gun Building => Topic started by: JCurtiss on October 07, 2015, 01:02:55 AM
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So, being new to flintlocks I just learned that the breach plug when tightened into the barrel must contact two (2) shoulders at the same time. One shoulder is in the base of the barrel where the breach plug threads stop and the rifling starts. The other shoulder is simply the end of the barrel.
The purpose, it seems, is to achieve two (2) metal-to-metal seals - one at each of the shoulders mentioned above, which seems difficult to achieve.
However, I've read that if the touch/vent/flash hole intersects the breach plug it's no big deal, merely grind a groove in the plug to allow the touch hole to communicate with the powder charge in the barrel. But in doing so, you lose one of the metal-to-metal seals. So presumably one (1) rather than two (2) metal-to-metal seals in acceptable?
Also, a face seal is not a very efficient seal for this application and trying to achieve two (2) of them simultaneously is beyond good engineering practice. Has anyone ever explored a single tapered metal-to-metal seal?
Perhaps a tapered seal is just too nontraditional for this application?
Am I asking too many questions?
Jason
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There's only one sealing surface, where the plug face meets the rifling.
Where the tang meets the end of the barrel is just a junction for a smooth transition from tang to barrel.
If you don't care to try it, just buy a barrel with the plug/tang already installed. If you like, you can remove the tang to check the seal, but it seems the better barrel makers get it spot on.
John
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I realize many originals and contemporary builders have positioned the touch hole back too far and had to notch out the breech plug! Many builders say that this increases velocity which it may HOWEVER in theory this is good but when cleaning in between shots black powder residue gets forced into the groove in the breech plug and reduces the chance of main powder charge igniting!! AVOID HAVING TO NOTCH THE BREACH PLUG AT ALL COSTS!! MEASURE AND RE MEASURE THE LAYOUT OF THE GUN DURING CONSTRUCTION !!
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My flinter had a touch hole that was too far back for good ignition, so I had a White Lightning liner installed, forward of the original touch hole and centered over the pan. In do so, the drill created a notch in the plug, and that worried me a bit. I agree that it's a bit difficult to keep it clean without removing the barrel and flushing water in and out. Should I assume that it's not dangerous? I suppose I could install a new breech plug, but that scares me, too.
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Thank you for the responses.
So if I've interpreted what I've read here correctly, the primary seal is between the plug face and the rifling face. Notably a secondary seal exists between the end of the barrel and the tang surface on the plug. However, this secondary seal becomes the only seal if the plug is notched to accommodate a touch hole that is drilled too far back on the barrel.
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If your plug is larger than the bore, you can get a shoulder to shoulder seal. It's nice to have, because it is so much easier to clean. Ideally, your touch hole liner will be ahead of the plug face.
The real seal is the labyrinth formed by the threads. If your plug is just thread depth larger than bore size, there is no shoulder. This is OK as long as your thread fit is good. Old taps and threading tools produced tapered plug and breech threads.
The tang shoulders are not a sealing surface at all.
If your touchhole cuts into the breech face, it's not ideal, but it's not unsafe as long as there is plenty of plug length.
I hope that helps.
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If your plug is larger than the bore, you can get a shoulder to shoulder seal. It's nice to have, because it is so much easier to clean. Ideally, your touch hole liner will be ahead of the plug face.
The real seal is the labyrinth formed by the threads. If your plug is just thread depth larger than bore size, there is no shoulder. This is OK as long as your thread fit is good. Old taps and threading tools produced tapered plug and breech threads.
The tang shoulders are not a sealing surface at all.
If your touchhole cuts into the breech face, it's not ideal, but it's not unsafe as long as there is plenty of plug length.
I hope that helps.
Acer,
From the view of a long time machinist I say you could not have said more or made it any plainer.
I thought about answering this but was tired from a day in the shop.
Bob Roller
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If by "single tapered metal-to-metal seal" you mean cutting the bottom of the breech seating surface at an angle (bevel) with an matching bevel around the OD of the threaded portion of the breech plug, Getz has been doing that for years. I think they drill the breech using a standard 118 or 135 degree drill point and then tap the treads.
David
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Your tap has a beveled lead, make your plug to match the bevel of the tap. It will fit right up tight.
It's not practical to have a tap with a square cut end, as the teeth break off with very little pressure. A tap's gotta have a beveled lead.
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There is a tutorial on fitting a breech plug. Go to Tutorials, Metal Shaping, and the third Herb post is "Fitting a Hawken Breech Plug by Hand".
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It's not practical to have a tap with a square cut end, as the teeth break off with very little pressure. A tap's gotta have a beveled lead.
You are correct, but that has not stopped me from grinding them square, over and over and over, you get the point! ;D
David
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I seat the breechplug threads coated with blue locktite. I have pulled breechplugs(easily) after 10 years and no gasses have gotten past the first 2 threads max if that. I once worked for days to get a perfect seal in both spots. Life is much easier now.
Turtle
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I seat the breechplug threads coated with blue locktite. I have pulled breechplugs(easily) after 10 years and no gasses have gotten past the first 2 threads max if that. I once worked for days to get a perfect seal in both spots. Life is much easier now.
Turtle
Notwithstanding that blue Loctite is a "mild" thread locker, I assume you had to apply heat and some muscle behind a 15-inch adjustable wrench to remove the breach plug?
On second thought, the blue Loctite requires only a nominal amount of torque to makeup the breach plug because you're no longer having to rely on a compression-fit metal-to-metal seal. So perhaps the necessary breakout torque was not too substantial after all?
What you're doing with the Loctite is creating a gas-tight seal and keeping the un-burned powder residue from packing-off in what Bob calls the thread "labyrinth". Notably a straight thread, which most all modern breach plugs and barrels seem to have, is useless for sealing unless a thread locker or other sealant is used.
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No, the plug comes out relatively easily with no heat. Blue is low strength locktite sealer and acts as a antisieze also-win win.
Turtle
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As Acer said, the ideal situation is to have a plug-on-internal-shoulder fit of the breach plug. This is ideal for 2 reasons: it is easier to clean and it prevents the ingress of fouling into the space between the male and female threads where corrosion can occur.
If you don't have a face-on-internal-shoulder fit then the threads will serve as a seal of sorts because the length of the thread exceeds the MESG for the burning powder gases. MESG = Maximum Experimental Safe Gap; which is the maximum gap over length ratio to achieve quenching of a deflagration. Even the old-time threads exceeded the MESG, although I doubt that the old-timers knew that's why their breech plugs didn't spurt flame and hot gas.
When I fit a plug I don't worry about tapping all the way to the shoulder, I file the first thread on the plug completely off so I have a nice plug-on-internal-shoulder fit. For 60 degree threads, as long as there are 5 complete threads the threads are as strong as the male shaft in tension. I then polish the face of the plug down to 1500 grit. I apply filler to the threads and turn it in. If (usually since) there is a small gap between the breech plug shoulder and the end of the barrel I just give the gap a stout rap with my hammer. The metal is upset and fills the gap. A few strokes of the file finishes the surface and we are done!
Best Regards,
John Cholin
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It's not practical to have a tap with a square cut end, as the teeth break off with very little pressure. A tap's gotta have a beveled lead.
Actually, it is practical, but maybe some folks only have one tap. I tap with a regular tap and then follow up with a bottoming tap. Then I use a flat ground one to clean the taper up. I do this a little at a time, working the tap back and forth until I hit bottom and have a flat shelf. I have never broken a flat ground tap.
People come from a variety of backgrounds, most of which are not tool related. With over 4 decades of experience as a mechanic, I learned early on how to judge the strength of the materials I am working with. It is much easier to do it right than wasting valuable time extracting broken bolts, taps, etc. This only comes with experience.
the ideal situation is to have a plug-on-internal-shoulder fit of the breach plug
One of the problems is that no one is taking the time these days to make good quality plugs for sale such as the one pictured. You will notice that the end of the plug is turned to eliminate the first thread, and also that it is threaded completely to the bolster which negates have to countersink the end of your barrel to accommodate those last missing threads. You can solve this problem a bit by turning your die over so the flat side does the cutting and clean those last threads up a bit. Of course, Acer will say that you will break those threads off your die. Right?
(https://americanlongrifles.org/forum/proxy.php?request=http%3A%2F%2Fi102.photobucket.com%2Falbums%2Fm104%2FML-L%2FALR%2Fbreechplug_zps3nm7zxm9.jpg&hash=41d5706b00ca8895ab5eeecf7661467dc8d48253)
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I'm not going to argue with you, TOF.
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I'm not going to argue with you, TOF.
Why would you even think you have to. Arguing is pointless, especially when one loses one's temper in the process. However, spirited debate is something I love and seek to engage in. Everyone learns something in the process. Sadly, in today's society, few are unable to distinguish between the two.
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It is sometimes difficult to tell the two apart in print on a computer screen........ we can't see the twinkle in your eye!! :o ;) ;) ;D
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For 60 degree threads, as long as there are 5 complete threads the threads are as strong as the male shaft in tension.
Long John - am I reading this correctly that the breech plug only needs 5-complete threads to have a strong/safe breech plug fit? The barrels I have used, along with the breech plugs have had about 10-threads. Is this just a CYA thing? I know that the originals always seem to have either the touch hole or the drum much closer to the breech end of the barrel than I see contemporary rifles having. I have often wondered about the breech plug depth and how short of a plug would still be safe.
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Thank you all for the lively and informative discussion on breach plugs and their sealing mechanism. And true to forum behavior, there are diverse and relatively passionate ideas about the quantity and quality of seals between the breach plug and barrel.
I now feel that I can make an informed decision regarding the installation of my own breach plug when that time comes. I ordered an Andrew Verner gun kit recently and hope to receive sometime next week and certainly look forward to working on the breach-plug-to-barrel interface as well as the rest of the kit.
Best,
Jason
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It is sometimes difficult to tell the two apart in print on a computer screen
Tim,
That's why I came up with my philosophy of "Measured Indifference" when dealing with internet posting. Whatever is said isn't worth arguing or getting upset over. Sometimes just stating the obvious precipitates that.
........ we can't see the twinkle in your eye!!
Yeah, but having known me longer than most others here, you know it's there and I will always play the Devil's Advocate.
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i have a relatively new smoothbore that has an unlined touch hole that intersects 2 threads of the breech plug. a small groove was filed into the plug face to route the pan sparks to the main charge. this became an issue, with unreliable firings because that plug face groove was simply too shallow to allow positive touch hole cleaning.
too shallow and short ...
(https://americanlongrifles.org/forum/proxy.php?request=http%3A%2F%2Fi.imgur.com%2F5PPlLHm.jpg&hash=fb50c710370b5249b48d547a2c56eed60f3ef66c)
i pulled the breech plug and used a dremel to open that channel, replaced the plug with anti-seize lube, and ignition became 100% reliable.
just right ...
(https://americanlongrifles.org/forum/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FGAxKpZC.jpg&hash=7de332e51687707e06655e46037293f42c8d0d48)
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I'd never say 'five threads is all you need' for a breech plug. Coarse threads are stronger than fine threads, because there is more metal engaged.
I know there were guns made with short plugs two hundred years ago. Some of those rattle in the breech, and can be unscrewed with two fingers.
I don't like to make a short plug, so I usually use what the barrel manufacturer makes.
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The threads only clamp the plug against the shoulder and give the strength needed to contain the explosion. Modern threads have enough tolerance to allow gas and fouling back into the threads 3-4 threads if the breeching allows. Either a gap of a groove filed in the brech face for the vent/liner. If the plug is properly fit there is no gas leakage into the threads.
Nor were all original plugs tapered. But when the tap makes the screw plate or the screw plate makes the tap then there is a close thread fit.
If the propellant is BP fouling in hidden areas is not a huge issue. But if the powder contains chorates which produce what is basically table salt when fired this something else. This stuff can dissolve steel with no apparent rust and will so so under an oil film. So having it trapped in breech threads or any where else is bad.
Once upon a time I had a vent liner gas cut the threads due to loose fits. A nipple without a seat at round section above the threads may well do the same thing.
Dan
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Dan, I assume black powder does not produce chlorates, but some BP substitues don't? I recall using Pyrodex in a xxx gun, and I could not get the bore to stop rusting. When I switched back to BP, problem went away.
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Coarse threads are stronger than fine threads, because there is more metal engaged.
Actually, that's typically not the case. A fine threaded connection is typically stronger than a coarse threaded one. A fine thread has a greater cross-sectional area at the thread root as compared to a coarse thread, which is cur deeper.
So if you subjected a UNC (unified national coarse) bolt and a UNF (unified national fine) bolt to a tensile test, the UNC bolt would fail at a force lower than the the UNF bolt, because the UNC has less area to support the load. Imagine 7/16" diameter thread root compared to a 1/2" diameter root, obviously the 1/2" is stronger in tension.
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Dan, I assume black powder does not produce chlorates, but some BP substitues don't? I recall using Pyrodex in a xxx gun, and I could not get the bore to stop rusting. When I switched back to BP, problem went away.
T7 is apparently non-corrosive or at least has no chlorates. The various sugar powders do not either. I have seen heavy deposits of BP fouling in breeches that did not rust. One was cleaned with water and the other I don't know about but suspect it was not water by the level of fouling in the breech and vent. But in both cases the fouling was oiled and cut off from oxygen in that way.
I have no experience with the sugar powders. Basically there is BP, P-dex and T7 the rest are various remakes of sugar based powders of the 19th c.
Again this is Bill Knights territory.
This will explain to some extent the various "sugar" powders.
http://www.laflinandrand.com/madmonk/clear_shot.pdf
http://www.laflinandrand.com/page3.htm
Dan
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gibster,
Acer's observations are correct - I should have qualified my statement that for UNC threads 5 full threads results in a threaded area that is equal to the cross-sectional area of the minor diameter of the male threaded element. At that area ratio the threads in sheer are as strong as the male element in tension. That's why commercially available nuts aren't any longer than they are - they only have to be as strong as the rod represented by the male screw at minor diameter.
Most commercially available breech plugs will come with 5/8-18 threads of 3/4-16 threads which are UNF. I'll do the calcs on how many threads for UNF you need for equivalent strength. It is less than the minor diameter of the male thread but I'm not going to work off memory - I have to do the calc.
Best Regards,
John Cholin
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So, being new to flintlocks I just learned that the breach plug when tightened into the barrel must contact two (2) shoulders at the same time. One shoulder is in the base of the barrel where the breach plug threads stop and the rifling starts. The other shoulder is simply the end of the barrel.
The purpose, it seems, is to achieve two (2) metal-to-metal seals - one at each of the shoulders mentioned above, which seems difficult to achieve.
However, I've read that if the touch/vent/flash hole intersects the breach plug it's no big deal, merely grind a groove in the plug to allow the touch hole to communicate with the powder charge in the barrel. But in doing so, you lose one of the metal-to-metal seals. So presumably one (1) rather than two (2) metal-to-metal seals in acceptable?
Also, a face seal is not a very efficient seal for this application and trying to achieve two (2) of them simultaneously is beyond good engineering practice. Has anyone ever explored a single tapered metal-to-metal seal?
Perhaps a tapered seal is just too nontraditional for this application?
Am I asking too many questions?
Jason
First traditional gun making is not "engineering practice" its gun making. Engineers and machinists are not gunsmiths and many times do not understand the reasons for why things are done as they are. I am sure some engineer or machinist, for example, decided that it was more efficient to install TC "Hawken" breeches to high torque that stretched the rebated section so that if removal was attempted the rebate would break off. But it was "efficient" from the standpoint of modern manufacturing.
"Not very efficient?" Yeah its a lot of work especially the first time or two. But one must remember that by MODERN standards a FL is horribly inefficient. Both is operation and in construction which is far more labor intensive than a modern designed to be made with minimal labor.
The face seal is actually very efficient when done right and perfectly seals the threads from any gas/fouling intrusion or in some cases gas leakage that can actually cut the threads.
A tapered, i.e. pipe thread will seal gases and liquids, however, it LEAVES FOULING TRAPS since the threads are invariably deeper than the plug this is VERY dangerous give the corrosive properties of some propellants used in ML arms.
Given the leakage inherent in modern thread tolerances and the possibility of chlorate fouling from a propellant its a huge mistake to allow gas intrusion into the threads or any fouling trap at the breech even if building a FL since people use it in FLs with a BP booster charge.
Our modern materials and tolerances designed for mass production and interchangable parts sometimes produce problems that were not seen back in the day. AND there were problems back in the day. People killed or injured by breech failures for example. The idea of royalty being killed was likely the reason Europeans set up proof laws.
There are things that worked well in the past with more ductile materials, i.e. iron as opposed to cold rolled steel, allowed things like unsupported drums in drum and nipple guns. With the materials used for these today an unsupported drum will sooner or later break off and depart at significant velocity. This is not supposition. So when we speak of doing things as they were done in the past, tapered breech threads for example, we have to under stand that compared to a propellant with high levels of Potassium Chlorate. There are various horror stories out there. Things that Mad Monk told me would happen decades ago have occurred. I.E. pits eating their way out to cause gas escape. People talk of originals with no shoulders, this is true. But BP is relatively benign and so long as the barrel is not threaded deeper than the plug. This error is not uncommon in modern ML barrels sold to builders with breeches installed. This enhances leakage into the threads and creates a fouling trap/patch grabber at the breech if tapped deep enough.
Cutting grooves in breech faces also produces leaks and traps. Its bad practice.
Dan
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First traditional gun making is not "engineering practice" its gun making.
Yes, I'm quickly understanding this to be the case.
A tapered, i.e. pipe thread will seal gases and liquids, however, it LEAVES FOULING TRAPS since the threads are invariably deeper than the plug this is VERY dangerous give the corrosive properties of some propellants used in ML arms.
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I would never consider a tapered pipe thread (NPT) for a breach plug. Instead I was suggesting a straight thread with a tapered seal surface on the nose, similar to this:
(https://americanlongrifles.org/forum/proxy.php?request=http%3A%2F%2Fi245.photobucket.com%2Falbums%2Fgg59%2Fjason_curtiss%2FTapered%2520Seal.png&hash=cbe25c62ed79525c3fe4f308dc07d994d37218b9) (http://s245.photobucket.com/user/jason_curtiss/media/Tapered%20Seal.png.html)
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This is a timely subject in my build. I have decided on no touchhole liner so my mark is just 1/16 forward at the breech face. I have not drilled yet. What IS the best practice for a lock inlet a bit too far rearward of the ideal touchhole?
My understanding is to drill just outside the breech face, regardless of if the hole is centered on the pan. Would this be the correct way to go? I have the sunset position correct, my hole is still in the pan, but the pan is 3/32 off center rearward. Any thoughts?
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This is a timely subject in my build. I have decided on no touchhole liner so my mark is just 1/16 forward at the breech face. I have not drilled yet. What IS the best practice for a lock inlet a bit too far rearward of the ideal touchhole?
My understanding is to drill just outside the breech face, regardless of if the hole is centered on the pan. Would this be the correct way to go? I have the sunset position correct, my hole is still in the pan, but the pan is 3/32 off center rearward. Any thoughts?
Firstly, I’m no FL builder.
But, for the touch hole location in the barrel, I would center it vertically on the barrel flat and 0.060” horizontally away from the face of the breach plug.
If the touch hole is too far forward relative to the pan when the barrel is installed, I would simply set the barrel back until it is dead center with the pan.
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First traditional gun making is not "engineering practice" its gun making.
Yes, I'm quickly understanding this to be the case.
A tapered, i.e. pipe thread will seal gases and liquids, however, it LEAVES FOULING TRAPS since the threads are invariably deeper than the plug this is VERY dangerous give the corrosive properties of some propellants used in ML arms.
I would never consider a tapered pipe thread (NPT) for a breach plug. Instead I was suggesting a straight thread with a tapered seal surface on the nose, similar to this:
(https://americanlongrifles.org/forum/proxy.php?request=http%3A%2F%2Fi245.photobucket.com%2Falbums%2Fgg59%2Fjason_curtiss%2FTapered%2520Seal.png&hash=cbe25c62ed79525c3fe4f308dc07d994d37218b9) (http://s245.photobucket.com/user/jason_curtiss/media/Tapered%20Seal.png.html)
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As a machinist that would design would be a major PITA to fit. If you are using the flat bottom of the barrel threading any part of the taper projecting into the bore would be a fouling trap. That design is to fit into a tapered seat with the Hex portion shoulder standing away from the surface. Square shoulder to square shoulder is the most practical way to mate plug to barrel. Both are measurable where a taper is very difficult to measure.
But from some of the original breechplugs to barrel fit I have seen we all may be over doing it. I admit to being spoiled by having access to a lathe to fit plugs. ;D
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read all the post, enjoyed them all. only way to completely seal a breech plug is to use a false breech plug. think about it folks.
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(https://americanlongrifles.org/forum/proxy.php?request=http%3A%2F%2Fi245.photobucket.com%2Falbums%2Fgg59%2Fjason_curtiss%2FTapered%2520Seal.png&hash=cbe25c62ed79525c3fe4f308dc07d994d37218b9) (http://s245.photobucket.com/user/jason_curtiss/media/Tapered%20Seal.png.html)
[/quote]
That design is to fit into a tapered seat with the Hex portion shoulder standing away from the surface.
[/quote]
Now you understand.
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Can we make this any more complicated?
Tapered seats? No reason. Makes the plug longer for a given number of threads and requires tooling the assure the tapers will mate.
Flat works fine.
Sealed
(https://americanlongrifles.org/forum/proxy.php?request=http%3A%2F%2Fi72.photobucket.com%2Falbums%2Fi199%2FDPhariss%2FBreeching%2FBreechface.jpg&hash=46517b71d2ebc5bf4a7cd87c57a51a7cebf9f4d7)
(https://americanlongrifles.org/forum/proxy.php?request=http%3A%2F%2Fi72.photobucket.com%2Falbums%2Fi199%2FDPhariss%2FBreeching%2FIMGP1064.jpg&hash=ef6cf9a6f4fdc8f54863cd41124918670daa6760)
(https://americanlongrifles.org/forum/proxy.php?request=http%3A%2F%2Fi72.photobucket.com%2Falbums%2Fi199%2FDPhariss%2FBreeching%2FS1100014.jpg&hash=661585e0db2c25e6cbdf20a1e3a3457b1f2901d2)
Not.
(https://americanlongrifles.org/forum/proxy.php?request=http%3A%2F%2Fi72.photobucket.com%2Falbums%2Fi199%2FDPhariss%2FBreeching%2F50calbreech.jpg&hash=6a3fbe5688f7f8a285a4668bc86bdb51a11bc55e)
Dan
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read all the post, enjoyed them all. only way to completely seal a breech plug is to use a false breech plug. think about it folks.
A 'hook breech' could be described as a false plug.
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A Rolls Royce engineer once said "We find complicated solutions to simple problems"
Turtle
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The idea of having a perfect seal never came along until the last 50 years or so. I have unbreached a lot of original 18th and 19th century guns that never even seated in the barrel at all. That alone doesn't prove much but all the ones I unbreached never had any dangerous corrosion or anywhere near it. The one thing they had in common seemed to be that the threads were very tight fitting and sort of a forced fit. Some gunsmiths of today are out to prove that they are somehow superior by advocating perfection to the umpfh degree. This is not true in all cases. Some are just over cautious or paranoid and others are truly out for perfection. In any case I don't think the seated plug is at all necessary and I usually just make a tight fitting plug with strong threads and seal it with plumbers pipe thread sealer.
I tend to be in the same school of thinking as Acer or Bob Roller. As long as it is safe and the residue can't penetrate the threads what can happen? In any event it has worked for two or three hundred years and maybe longer. This doesn't mean I never seat a breech plug. I just don't think it's a life or death deal by far. I have never seen a original shotgun that had seated plugs. I mean no seat at all.
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The idea of having a perfect seal never came along until the last 50 years or so. I have unbreached a lot of original 18th and 19th century guns that never even seated in the barrel at all. That alone doesn't prove much but all the ones I unbreached never had any dangerous corrosion or anywhere near it. The one thing they had in common seemed to be that the threads were very tight fitting and sort of a forced fit. Some gunsmiths of today are out to prove that they are somehow superior by advocating perfection to the umpfh degree. This is not true in all cases. Some are just over cautious or paranoid and others are truly out for perfection. In any case I don't think the seated plug is at all necessary and I usually just make a tight fitting plug with strong threads and seal it with plumbers pipe thread sealer.
I tend to be in the same school of thinking as Acer or Bob Roller. As long as it is safe and the residue can't penetrate the threads what can happen? In any event it has worked for two or three hundred years and maybe longer. This doesn't mean I never seat a breech plug. I just don't think it's a life or death deal by far. I have never seen a original shotgun that had seated plugs. I mean no seat at all.
The last breech plug I installed was in a GM 50 caliber with a 3/4x16 thread. I used a depth micrometer to see how deep the threads went and the made a plug that was .005 longer and screwed it in tight. I removed it to see if the crush was OK and it was so I milled it to shape in the barrel and it's been there ever since.I used a travel indicator on the lathe to establish the .005 extra length. I think the idea is to have an easily moved ball or bullet and a plug that is impossible to move. I never thought of a pipe thread and prefer to use what I KNOW will work safely.
Bob Roller
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wrought iron barrels and wrought iron breech plugs, with a slight taper have stood the test of time. I have a box full of them I cut off old WR barrels at the breech. only thing that sealed then was the threads. erosion was minimal on plug and barrel
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(https://americanlongrifles.org/forum/proxy.php?request=http%3A%2F%2Fi245.photobucket.com%2Falbums%2Fgg59%2Fjason_curtiss%2FTapered%2520Seal.png&hash=cbe25c62ed79525c3fe4f308dc07d994d37218b9) (http://s245.photobucket.com/user/jason_curtiss/media/Tapered%20Seal.png.html)
That design is to fit into a tapered seat with the Hex portion shoulder standing away from the surface.
[/quote]
Now you understand.
[/quote]
So that plug is either a Sae or a JIC plug, and it'll work fine on a hydraulic system or the like. Usually they are hollow in the front section? I guess you're suggesting making something like it, but I don't see the benefit over a standard plug. And trying to mate the tapered plug portion to the tapered barrel bore section while try to mate the rear of the barrel to the front of the tag section would be a lot more difficult, to no great advantage.
John
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Dave Crisalli is a graduate of Annapolis and an expert at ordinance. I believe he will tell you that no thread or so called seal will seal at the pressure of a rifle chamber. Maybe he will give us some insight here.