Seating a breech plug

[aross007]

I'm new to this forum, and find it fascinating.  I've built up a few guns, starting with one that would have looked better if made from a cedar fence post and a length of gas pipe.  I now have a couple that I don't mind people seeing, although nothing as good as what I see here.  My question is: when I seat a breech plug I want it to end up tight at both the end of the barrel and at the bottom of the hole, right?.  My problem is that the tap doesn't cut all the way to the bottom, nor does the die cut all the way to the shoulder of the plug.  I find myself filing the threads off the end of the plug, and grinding off some of the threads in the barrel.  Am I missing something? 

Thanks for the sharing that you folks do,
Alan

[Dennis Glazener]

First off welcome to ALR, hope you enjoy your stay.

You need a bottoming tap so the threads are cut all the way to the bottom of the hole. You can buy these or if you have the tools grind your existing tap square across the bottom at a point where you have full threads the full length of the tap. Be careful when you use the bottoming tap so you do not break it off when you get to the shoulder.

You will either have to remove the first thread (or most of it) in the barrel or if you prefer you can remove the last thread on the breechplug. I remove the one on the breech plug.
Dennis

[whetrock]

Welcome Alan,
Here's an old thread you may want to see.
http://americanlongrifles.org/forum/index.php?topic=24730.0
You should be able to click on the link to open it.

As Dennis said, you need to cut the threads deeper. If you are installing your own breech plug, then the barrel you are starting with probably doesn't have the threads all the way down. They are assuming that you will do that.

There is a very good review of how to do that on the TOW website. Here's a link to that.
http://www.trackofthewolf.com/Categories/PartDetail.aspx/1012/1/LABOR-BP
You will note that their instructions also mention the fact that the last bit of the last thread of the tap will sometimes snap off. That’s normal and it’s not a big deal. Easy to grind it back to shape for the next time you want to use it.

Because the last bit snaps off, I have found it helpful to have a couple or three taps ground to suit various steps in the tapping process. The first and second taps have various amounts of taper showing, but the last one is basically a cylinder ground flat on the end. And that's the only one that gets the broken thread. And since it is already flat on the end, it is easy to sharpen it by just grinding the end flat again until sharp thread is all the way to the end and a full thread ends at a flute. I just started with regular shaped taps and ground off the pointed ends until they were the shapes I needed.
Use plenty of oil or cutting fluid and clean them frequently while tapping.

Dennis mentioned cutting back the last thread. This is what they call “thread relief” on the TOW site. They discuss the option of relieving the last thread. They also mention that some plugs (those made on a lathe) often have the thread closest to the tang relieved a bit. Thread relief just means cutting a thread back so that it doesn't cause trouble. If you want, you can cut back the last thread. But in my opinion, it's best not to be rounding back any threads other than perhaps the last one.

Whet

[Bob Roller]

Get a bottoming tap for whatever thread you're dealing with and try to grind it flat across.
Turn the die around and it should bring the last thread closer to the plug.

Bob Roller

[smallpatch]

Well, I've breeched more than a few barrels, and never used a bottoming tap.  Plugs today are way too long today for "safety" concerns and liability. It definitely will not hurt if the first and last thread don't seal perfectly. You've got at least 7 or 8 that are still complete.

I simply mark the plug with either a magic marker or dyechem and alternately mark and file till both the plug and breech lug snug up together.
Just make sure to leave the breech plug face flat and polished, it will seal well, and clean easily.
Hope that helps.

[aross007]

Thanks for the quick and helpful replies - I'm sure to be back with more questions

Alan

[whetrock]

Small patch is quite right to emphasize the thread count. If we are talking about safety, then thread count is the main issue.
Modern plugs as sold are quite long. And breeches as sold on most barrels are quite long. There are two reasons why they are long. The first is liability—safety from the perspective of lawyers. The second is thread relief. Threads that have been relieved are no longer there. So, (talking only about simple plugs here) a long plug that has been relieved is basically a short plug with two useless bits of metal on either end, doing nothing other than serving as an unfortunate reason to move the touch hole forward (or the breech end of the barrel and tang backward, depending on how you look at it.)
In other words, if you are happy to use a long breech plug, then maybe you can afford to loose some of the threads to thread relief.
That said, if you want a shorter breech overall, so as to approach something more like the architecture of the old guns and still maintain a healthy margin of safety, then you need to carefully consider thread count. A shorter plug has fewer threads, and so every thread becomes important.
So, once we have established that there are enough good threads for safety, then the remaining issue is all about architecture. Moving the touch hole forward in relation to the tang ultimately affects architecture.
What we don’t want is a short plug with missing threads. Whether a guy is using a long plug with thread relief, or a short plug with full threads, either way we want to see an appropriate number of good threads making full contact. And we want to see the face of the plug mating up fully with the shoulder inside the hole, etc., just as smallpatch mentioned.

[aross007]

long plug, and the touch hole will be into the breech plug.  This project is just a flintlock barrel to convert a T/C Hawken, but I've had the same issue/challenge with almost all of my builds.

Thanks again,
alan

[Bible Totin Gun Slinger]

Mine would have been easier if I would have had a 4 jaw chuck for the lathe. But in the end it turned out perfect.
I figured they made them Breach Plugs so long was so you could cut it off as needed. Mines a hook breach so no shoulder.
Bottoming Tap was not needed.
My machinist took advantage of the long breach plug and shaped the front so the fire from the flash would shoot into the charge better.

[whetrock]

Yeah, on a regular breech plug there are 2 shoulders that have to mate up. One is the shoulder on the tang. The other is the shoulder inside the hole.

The shoulder on the tang is just cosmetic. It should mate up with the end of the barrel, but even if it didn’t touch at all it would not affect safety. Hooked breeches don’t even have that one as part of the plug.

Then there is the shoulder inside the hole. That one does matter. Almost all ML barrels have that one. (As far as I know the only ones that don’t are barrels such as some pistol barrels and cannons and mortars that are bored from solid material and made as a blind hole, without a breech plug.)

The face of the breech plug needs to mate up solidly with that shoulder inside the hole. The shoulder can be flat (perpendicular to the bore) or slightly cone shaped, either way, but it should be smooth and have no gaps, chips or rough chatter from drill bits, mill heads, etc. that would leave a gap that would lead to gas leakage. The face of the plug is supposed to close it off completely.

Note that even if you use a plug with a cupped face, you still have a rim. That rim is the "face" that must mate up with that inside shoulder.

[Long John]

Alan,

While using a bottoming tap is one way to do it, I don't use one.  I file away one thread adjacent to the seating face of the breech plug.  If you have 5 full threads then the threads are just as strong as the plug and barrel wall; no real need for more threads than 5.  The front face of the breech plug is supposed to seal against the step inside the barrel where the bore meets the threads.  I use soot on the breach face to verify that there is a good seal all the way around.  The threads don't seal - they just hold that breech face tight against that inside step to achieve a seal.

I try to get the inside faces to seal when the outside shoulder of the breech plug tang part has a tight fit to the top flat of the barrel.  If there is a little bit of a gap between the top barrel flat and the tang should a well-aimed stroke from the hammer will close that up nicely.

The above works for me.

Best Regards,

John Cholin 

[Bob Roller]

This drawing shows the need of a bottoming tap. I once took out a plug that had a pipe thread
 and there was a substantial FOULING BUILD UP in a gap in front of the face of the plug. This was
 some sort of "jackleg"work by an unknown person.

 Bob Roller

[Acer Saccharum]

That undercut can be a place for fouling to collect; worse, for a glowing ember to be hiding during a rapid fire exercise.

[Dphariss]

3/4-16 taps ground for barrel breeching.



This is a breechplug seated to the shoulder properly. Note the imprint of the lands on the color on the breech face.



This is the barrel.


It will be final machined while on the barrel this was a long tang breech that could not be purchased.
It would look similar to this when installed if looked at from the inside.


This is what occurs when the barrel maker shortcuts the process as is far more common than many would think.


This is the plug.

This makes the gun impossible to properly clean. If used with "replica" powders with high levels of perchlorates its possible to have serious corrosion issues.
It looks like this when viewed from the bore of the barrel.


Looking past the rebate of the plug shows the threads in the openings formed by the grooves.

Dan

Got the plug photo so it shows now. Should have checker earlier but I am supposed to be doing gun work so I hit post and left...

[Bob Roller]

Dan,
That stub tap is a serious tool.I used to make some up when I helped Bill Large years ago.
Bill will be gone for 29 years on 23 September of this year.Seems like last week to me.
Thanks for showing the right way to breech a barrel.

Bob Roller

[Bob Roller]

That drawing shows a proper way to breech a barrel.The pipe tap I mentioned earlier was a tapered tap which is how pipes are sealed but the likely chance of getting a precise fit in a muzzle loader barrel with a pipe tap is not likely.That drawing is backed up by Dan's pictures and ANYone can understand them.

Bob Roller

[Pete G.]

And don't think for a minute that a barrel breeched by the maker is always correct. Check and re-check. I have a build right now that required another 1/4 turn for the face of the plug to make contact.

[Dphariss]

Dan,
That stub tap is a serious tool.I used to make some up when I helped Bill Large years ago.
Bill will be gone for 29 years on 23 September of this year.Seems like last week to me.
Thanks for showing the right way to breech a barrel.

Bob Roller

Its been reshaped and shortened a few times as you might guess.

Dan

[Acer Saccharum]

I like Dan's method. That's what I use. Kiss the plug face on the bore.

[E.vonAschwege]

The original question has been answered I believe, but here's a snapshot I took of a plug that I breached last week.  Notice you can see the grooves and lands clearly where the face has made full contact with the bore. 


-Eric

[Acer Saccharum]

Eric uses the toothed vise jaws that put the authenticity in every antique gun you come across. I'm glad he's such a stickler for detail. 

[E.vonAschwege]

Eric uses the toothed vise jaws that put the authenticity in every antique gun you come across. I'm glad he's such a stickler for detail. 

Nah - the teeth on that one are too large, I use my older fine-tooth vise to put proper markings in barrels and breech plugs   

[coutios]

   Eric, Fine job. Just the way they need to be.... Who wants to take on a .50 cal. with a .562 plug ? Photos please....
I hate that combo....

Dave

[Daryl]

Eric uses the toothed vise jaws that put the authenticity in every antique gun you come across. I'm glad he's such a stickler for detail. 

Nah - the teeth on that one are too large, I use my older fine-tooth vise to put proper markings in barrels and breech plugs   

A light 14 ounce ball peen hammer can make some wonderful authenticity wear and ding spots on metal surfaces. A ring of jail-house keys can make stocks look 200years old, quickly, but - I don't have access to those any more.

[whitebear]

Whetrock, can you give us a rule of thumb on the number of threads on a breech plug
and any variables that would change the # of threads?