why you can’t just cut back the face of breech plug

[whetrock]

An issue recently came up online that presents a bit of a safety concern, and so is worth a visit. (Safety is always worth another visit.) The issue is about cutting back the face of a breech plug so as to move the touch hole back, so as to attain a more “historically accurate” architecture.

The reason this is even considered is simply because some modern production barrels use a slightly deeper breech hole and longer plug than were used on some antique rifles. The result moves the breech of the barrel back slightly in relation to the pan, and as a result the fence of the pan doesn’t align with the back of the barrel. It is an aesthetic, rather than mechanical issue.

It seems that some new builders may mistakenly assume that the face of the breech plug can be moved back (so as to be able to move the touch hole back) simply by filing back the face of the plug without actually reworking the entire breech. But note that this is NOT an acceptable way to accomplish the goal. The result leaves a gap between the face of the plug and the shoulder at the base of the threaded hole. The gap creates a dangerous situation.

While it is true that some very qualified gunsmiths do use a slightly shorter plug, they do not simply cut back the plug and leave a gap. Rather, they rework the entire breech and plug arrangement. The size and length of plug required for safety depend the caliber of the firearm, the depth and pitch of the threads, the type of charge used, the rate of twist, the metals used in the barrel and plug, etc., etc. (In other words, this is not a place to just start tinkering around.)

Here are some images to help explain the problem.



Several good books on gun building describe how to seat a plug correctly, so I won’t elaborate further. (Peter Alexander’s Gs. of Grenville Co. chapter on “Installing the Breech Plug” also mentions how to repair an ill-fitted plug that was left with a gap.) Qualified gunsmithing services are also available for hire. (TOW will fit a plug expertly for the very reasonable fee of 25.00, and will happily fit a plug before they ship parts you order from their site.) And several barrel makers ship their barrels with plugs already installed properly, which is a good thing!

For some additional points on how a plug should be fitted, and the tooling required to do the job correctly, new builders may want to see TOW page on same. Helpful info to be had there: http://www.trackofthewolf.com/Categories/PartDetail.aspx/1012/1/LABOR-BP

[Dphariss]

or


Which works pretty good too and maintains more than 4 threads on the breechplug.
English lock designs are usually farther from center of pan to rear of fence than Germanic locks, I have read. Never paid any attention till I read that.
Dan

[Acer Saccharum]

If you look at a handful of original guns, you will see fence placement is pretty random. A few fences are in alignment with the breech end of the barrel, but just as many aren't.

I have shortened some plugs, because they were ridiculously long, but I really don't care about the fence alignment that much.

More importantly, a long plug causes the lock to be moved forward, reducing your options for lock bolt placement. If the lock is forward enough, it can cause the lockbolt hole to go thru the tang and skin the back end of the barrel.

[Dphariss]

If the breeching is done similar to this


Shooting causes this

This is more typical than some might want to think with some barrels that come breeched by the barrel maker as this one was.

Can

[Acer Saccharum]

This breech I made on one gun. It shot OK, but it was turrible to clean at the end of the day. I could shoot all day without cleaning, but I can do the same with a flat breech. No advantage that I could detect over a flat breech. I made it like this, thinking it would be faster ignition, but I am done experimenting with breech designs.

[Dphariss]

If you look at a handful of original guns, you will see fence placement is pretty random. A few fences are in alignment with the breech end of the barrel, but just as many aren't.

I have shortened some plugs, because they were ridiculously long, but I really don't care about the fence alignment that much.

More importantly, a long plug causes the lock to be moved forward, reducing your options for lock bolt placement. If the lock is forward enough, it can cause the lockbolt hole to go thru the tang and skin the back end of the barrel.

I don't duplicate guns with the fence much forward of the breech. I don't like the way they look. Though I have made rifles from precarves now and then that suffered from this.

Having the lock 3/8 or more forward can change the lines of the stock.
If trying to build a rifle that is visually similar to  a certain original rifle moving the lock forward (or back) will change a number of things to do with the wrist, the trigger and guard placement, where the lock panels end in the wrist. This can result in a rifle that does not look much like the original.

I would also point out that RCA and other picture books are full of rifles that are aesthetically unpleasant. Not every one who made rifles back in the day had a good eye for line.

Dan

[whetrock]

... maintains more than 4 threads on the breechplug. ...

You guys may notice that I edited the original picture and put in a note in the sketch emphasizing that I'm not intending to comment on number of threads necessary. There are some interesting "threads" (no pun intended) on that issue on this forum for anyone interested in searching.

[Acer Saccharum]

And yes, I've purchased breeched barrels, with fitted plug, and the plug face does not seal against the bore. A little like Whetrock's middle illustration.

This is not good practice, as it's a pocket for corrosion to collect. I don't think it's particularly unsafe, but it's not ideal. But for a barrelmaker to spend an extra half hour on an operation is something not everyone is willing to pay for. So it is up to the owner to check plug-to-bore fit BEFORE you inlet the barrel.

Just sayin'.

While you've got the plug out, run a patched ball down the bore to look for tight/loose spots, and roughness. If it's all good, proceed with fitting the plug tight up against the bore.

[Dphariss]

This breech I made on one gun. It shot OK, but it was turrible to clean at the end of the day. I could shoot all day without cleaning, but I can do the same with a flat breech. No advantage that I could detect over a flat breech. I made it like this, thinking it would be faster ignition, but I am done experimenting with breech designs.

I have a pair of these in a swivel breech. If sloshed with water its not significantly different than a conventional breech. I did make a stepped jag for it.


The key is plug the vent, pour in water and slosh buy upending the rifle 2-3 times. Wet patch then slosh again. This will remove almost all the fouling.

The chambers were made with a 3/8" ball end mill.
I did this to prevent using a liner in a thin barrel.
I don't think that a flat breech is slower than anything else and apparently is faster, the Nock design I sent to Larry P. times a little slower than a flat breech. But it should produce more velocity  and might get the projectile out the muzzle as fast or faster. However, to prove that would take a lot of work and a normal length barrel to test breeches in.
The Manton recessed breech is supposed to be faster. Since it reduces the distance from pan to main charge. But again this would need to be timed to confirm.
The Nock does have a lower variation apparently and this makes sense since it was primarily used in shotgun and consistency trumps speed when wing shooting.

Dan

[whetrock]

The images Dan posted of the damaged plug look to me like the hole may not have been threaded all the way to the bottom.

For any readers unfamiliar with this problem, the TOW page that I mentioned earlier (http://www.trackofthewolf.com/Categories/PartDetail.aspx/1012/1/LABOR-BP )
talks about that problem in their section on “Zero clearance bottom tap”.  As the TOW page notes:
“nearly all muzzle loading barrels are factory threaded for the plug. None are completely finished inside. Only the machine work is done. The final bottoming tap step must be completed by you, by hand.”

A bottom tap is a tap ground in such a way that it can cut to the bottom of the blind hole. It’s easy enough to make one by grinding back the cutting tip on a regular tap. Actually, though, I’ve found it worked best when I made a set of three, grinding them back in stages. A set of taps that cuts the bottom out in stages like that seems to work better for me than just trying to get there with one square bottom tap.

Some people try to skip that step of bottom taping the hole by just forcing the plug in tighter, as if hoping to more or less grind the plug down into the hole. Another common “cheat” is to round off the last few threads with a file. (That’s to say that if the hole isn’t threaded all the way down, then they try to get around the problem by just filing off the threads to match the incompletely threaded hole.)

Neither of these are good options. It’s best to bottom tap the hole, so that your plug can fill the breech hole completely.

[Acer Saccharum]

A dead flat ground tap will certainly lose its first few teeth when it bottoms fully against solid material. I always put a very slight bevel on the first teeth of the tap. Then I taper the plug accordingly.

If you try to jam the plug into an incompletely threaded hole, the threads gall, and upon removal, tears out chunks of thread. Then you don't have good thread fit once you clean the threads up.

It helps to slather some extreme pressure grease or anti-seize on the threads before assembly. This allows a little 'thread forming' while avoiding the galling of too close a thread engagement.

[whetrock]

I rummaged around in my junk box and found two old plugs that I ruined when I was first trying to learn how to seat plugs.

Image (a) shows a discarded plug, from a .45. This was from the first time I ever tried to seat a plug. I ruined it by filing back the leading edge. I discarded this plug and started over when a mentor showed me that I had ruined it. (It was only left with .29” of good threads—not enough.)




Image (b) shows another discarded plug, this one from a .50 cal. I still hadn’t understood how to bottom tap the hole. This one only had .36” of good threads. This plug was no better than the damaged one that Dan showed in an image earlier. You will see that this one was actually fitted to a stock. I thought I was well on my way when I heard, “Uh, sorry bud, but that plug won’t work. Got to redo that.” Painful, but it was enough to make the lesson stick.




Image (c) shows a plug that I pulled out of a .45 cal build in progress this morning just so as to make this post. (I hope new builders understand from that just how important I think this is!) This is a good fit. This is a machined plug with total depth of .60”. (That’s measuring from the shoulder of the tang to the face of the plug with a vernier caliper.) This sort of machined plug is often made with some thread relief at the rear, which means that that area has no threads, and so that part cannot be “counted” when you measure the length of good threads. This plug turns in by hand but has no wobble; only the leading edge of the deepest thread was rounded for fitting; it has good threads for a full .50” ; and the entire rim of the face of the plug mates with the shoulder at the base of the breech hole.



Whetrock

[Acer Saccharum]

'C' is what I build.

[WadePatton]

I'm having a hard time distinguishing the shoulder at the end of the bore-and this is likely because it's a 5/8 plug in a .54 cal.  It's "pre breeched" from the maker and all, but of course i've banged things up and welded on an extension and am now at the point where i want it nuts perfect.  (hazel nuts).  Would bottom-tapping it a bit help define the shoulder?  which of course is mostly lands.

I had to clean up shoulders (plug and bbl exterior) to get it back down to the witness mark, but then didn't get any clear touch marks inside.

I'll haul it down to John's and go over it with him before I take any scary risks for sure...somebuddy needs to get his buttplate on there.

whetrock, them tapered threads are for plumbing pipes.   

[Don Getz]

Whetrock..........how many barrels have you ever breechd?   From your dissertation I guess I have done them all wrong.
You state that the hole should be completely threaded all the way down to the flat bottom.  In order to do that you will
have to grind a tap to do it.........I wonder why you can't just buy one?  After you grind it down to that point, did you notice how fragile each one looks?  Even if you would do this, and if the points of each thread didn't break off, where
would that metal go to when you hit bottom?   Lets just suppose you are making barrels for a living, and you were to
tap each barrel like you would like it to be done,  how long do you think that "bottom" tap would last?  Maybe for a couple of barrels, but, you wouldn't need to buy a new one, just grind it down a bit again   Also will take a little longer to breech
it, if you want to get paid for your time, prices would have to go up.   If you think modern muzzleloading barrels have
breeching that is unsafe, you should take a look at some old barrels.   After doing that you will probably take up golf.
Don

[Acer Saccharum]

Don, what do you know about barrel making? 

[Acer Saccharum]

I have seen some originals with thread that would scare the hooie out of you. The plug rattles around so bad, it would unscrew if the bbl weren't stocked.

Don, I think some guys like to finesse their plug fits after purchasing(self included). From a machining standpoint, it's very fussy work to tap with a flat ended tap without chipping the teeth off. It's well nigh impossible to keep all the teeth intact unless you've ground a small bevel on the end of the tap. It only needs to be 1 thread or a thread and a half.

Bevel the plug end same as tap, and it will all go together.

[Dphariss]

Taps ground as the short one is will tap right to the bottom of the hole. However, if run right to the bottom the tap may make divots in the surface the breech face should seal against.


The need to tap right to the end of the counter bore is probably overrated unless the plug is short on threads otherwise. If there is plenty of thread engagement the threads on the plug can be cut back a thread or a little more as I did with this one.


The important part is to take the time to seat the face of the plug against the bottom of the counterbore. Note the imprint of the lands on the dye on the breech face.

 
So it looks like this when assembled.



If you just turn it down and run it up into the bore it will look like this, its possible to see into the threads by looking into the grooves.



This is fouling trap breech from the previous post with fouling packed down against the threads when removed.
The vent liner installation is unsupervised high school shop quality work as well.

Dan

[Dphariss]

Old barrels?
Some were done right, some were not (just like now). Many, from the vise tracks, have been reworked in one way or another over the years so it may have been breeched the last time by some blacksmith someplace..
I try to do things right.
I  shoot everything I make at least a few shots 5-10-20 and I like to know that the powder charge right next to my face is properly contained. That there are no oil/fouling traps to give the shooter reliability problems or make the gun difficult to clean or cause REAL corrosion problems if the owner is uninformed enough to use a propellant with Potassium Perchlorate as an ingredient. Like the fouling eating its way out to the point there is a gas leak.

Dan

[whetrock]

Don,
I certainly don't mean to contest your expertise. And I've never used one of your barrels. I have no idea how you thread them.

The only work I critiqued was my own. The first two plugs I put in the photos were done in what I now think of as a shoddy manner. That's because I did not understand at the time that the barrels I was using were not yet tapped beyond a minimum, and that they still needed some handwork.

I think there are a lot of new builders out there who don't completely understand what they are working with when they buy parts from a retailer. For example, it is quite clear from the questions that go up on the boards that a lot of guys have not yet learned how to tune a lock. Some seem genuinely surprised to discover that a lock might need a little extra work after they receive it in the mail. It’s not a problem. It’s just part of the learning curve. So we spend a lot of time on here talking about how to tune a lock.

In a similar manner, all I'm talking about here is how to "tune a breech". I only mean to point out that the breech of a barrel may need some additional hand work after a guy receives it. Just as a lock might.

I’m not meaning to suggest that professional barrel makers need to change their practice. But I am meaning to point out that builders need to examine the breech of barrels they buy, and they need to be prepared to do some handwork on the breech. (That’s all the TOW page I cited earlier said, as well.)

By the way, I would be quite happy with the threading Dan showed in the last images he posted. I appreciate the clarifications and additional explanations Dan and Tom have added to the thread.

If the emphasis on safety I tried to give my posts came across as arrogance, I certainly apologize.

Whetrock

[Acer Saccharum]

Guys, the written word is very subject to various interpretations. The writer may have one thing in mind, yet the reader might put their own spin on the words they see.


When you receive a barrel, there are some things that YOU, the purchaser should do.
1) De-breech it, and run a tightly patched ball down the bore. This tells you that the bore is ok or not. (several posts over the years the builder discovers a bad bore after the rifle is all assembled.)
2) Inspect the breeching. fix it if it's not to your liking. ( do this before you inlet the bbl, you don't want to move the bbl back 1/16 after the touchhole/keys/tenons have been located)
3) Drawfile the side flats before inletting bbl. I like a little draft on the side flat, halfway down, so barrel comes out of channel easier.*

DID....stands for what? De-breech, Inspect, drawfile.....

Happy New Year!

*a Rich Pierce suggestion.

[deertracker]

I appreciate everyone's contribution to this thread. I've learned a lot. Thank you.

[mark esterly]

ok here's the scenario.  i buy a top quality barrel from a well respected skilled craftsman like mr. getz or rice barrel and have a skilled smith install the plug because i don't trust my skill at such an important area as the breech. now i'm supposed to debreech it. run a patched ball through it ( when i'm not sure yet which size ie. .490 or .495, .567 or .570 etc. ect. is suitable) to make sure the bore and the plug is good. then rebreech it hoping i don't mess it up?  all before i inlet the barrel into the barrel channel.
     that indicates to me that you don't think any of the barrel makers or smiths know what they are doing.
     

[Dr. Tim-Boone]

If I buy a Getz, Colerain, Rice, Long Hammock or other barrel and the supplier says I am paying for a breeched barrel, I expect it to be done properly and to fit tightly. So far everyone I have bought has, when debreeched just for safety/QA purposes they have looked fine. putting some black magic marker on the breech to see how the plug mates with it has been prety convincing....and, I will keep doing it......

[rich pierce]

De-breeching and checking a barrel is not a big deal.  We're supposed to be gunsmiths or trying to be.  Who wouldn't do a quality control check on their lock but just assume it sparks, doesn't have friction issues, or frizzen timing problems?  Same with basic barrel QC.  It detects/avoids possible problems which are readily fixable before going further.  If I have to take a little off the breech and move the plug to the next flat, no big deal- now.  If I detect a problem after the barrel is inlet and the dovetails in, BIG PROBLEM.  Do I trust barrel makers?  Yes, I admire their skills, trust they're human, and trust they are not perfect every time.  A patch-grabbing, crud-collecting breech is really a pain and not something I'd enjoy or want to pass on to a customer, same as a poor-sparking or slow lock.