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I didn't know how to fit a plug on my first build, it was Rice barrel that probably had a perfect fit but it was so hard to remove the plug I was sure something was wrong and started filing. I jockeyed back and forth filing the plug and breech face and re-fit what was probably a very good fit before I touched it.

My next was a Colerain with what was supposed to be fittted from the factory but the plug didn't come close to being seated, I learned more before I got the plug in correctly.

Next was a GM barrel with very deep threading in the breech that put my touch hole way too far down the barrel to suit me. Out with my files again.

I didn't have any experience, I only used files but went slowly and everything came out ok.
 
The breech plug is drilled and threaded as to depth being the width of the plug. The other parameter is the end of the plug , should touch the end of the drill , and tapped breech plug hole in the barrel. This was iterated to me by Dick ,and Donny Gets , back in the beginning of my journey. Log cabin Shop has a gunsmith that can perform this task for you. You should get their catalog any way.. Good people..........oldwood
 
It amazes me that every time someone asks a question like this it always goes to you have to have a lathe to do it. Not everyone can afford to spend thousands of dollars for a lathe. Not every one has access to someone who has a lathe that would be willing to set it up for a single job. All these things were done by hand with simple tools for hundreds of years. I would suggest getting a book or two on building rifles they will have a chapter on how to breech a barrel.
 
With experience , lathes , and drill presses aren't needed for most operations building a m/l gun. For seating a breach plug , a file , hack saw, , and if ya want to get crazy , a bottoming tap could make it easier. If ya gotta couple of tools , no matter how messed up a breach plug install is , a half hour gets it done . .......oldwood
 
Picked up a .45 rifled pistol barrel and plug. The threads in the barrel end about 1/4" before the plug is fully seated.
I'll have to have a machinist fix this up for me but which way should I go.........

Cut the threads in the barrel deeper?
Grind the plug back to match the threads in the barrel?
Make a shim?
Combination of the above?

Obviously will have to trim the barrel shoulder.


View attachment 208205View attachment 208206

If the length of threads are square to the diameter of the plug threads it'll be as strong as it's ever going to be.

Example- 5/8ths plug 5/8ths threads.
 
Over threading is not the issue. You can't have a void as shown here. The OP said the threads were not completed to the shoulder. Thanks for your reply
LarryView attachment 208380
That makes no difference whatsoever. They aren't threaded to the shoulder on a breech plug.
1679497379959.png
 
Last edited:
That makes no difference whatsoever. They aren't threaded to the shoulder on a breech plug.
View attachment 208480

Your photo does not show the sholder in the barrel. The plug must seat on the counter bore shoulder! Please see figure 3 from National Muzzleloading Association
Larry



Installing a Breechplug | The Apprentice’s Notebook Part 1


Muzzle Loader Building, Muzzleblasts, Muzzle Blasts Archives

The Apprentice’s Notebook​

Installing a Breechplug
By Jay T. Close, Kentucky

INTRODUCTION​

A good measure of your rifle's safety, reliability and durability de pends in how the breech plug is installed. Fitting that plug is not a job to be taken lightly but it is how I usually begin a rifle. If I do a good job here, I can approach the rest of the rifle with confidence that the finished gun will be a safe one. If you're intimidated by this work, some manufacturers -- e.g. the Getz Co. -- sell barrels already breeched. You can be assured of this work. Also, if you buy a barrel and breech plug from Track of the Wolf, they'll install the plug for a modest charge. They too guarantee the work is done right. Nevertheless, the only way to learn to install a breech plug is to fit a few. Moreover, installing a breech plug is a very basic skill, certainly, one required of anyone aspiring to the appellation of "gunsmith". So, buy a barrel and a breech plug to match the barrel threads. You'll minimize frustration if you purchase one of the so-called premium barrels. These have the exterior of the barrel-shaped con centric to the bore and allow you to match the tang of the breech plug to any of the eight flats of the barrel.

GETTING STARTED​

Breechplug_Fig1.jpg

Figure 1 shows a schematic of a common breech plug with its various parts named. When you buy a barrel and breech plug make sure that the threads of the two components match. Be careful here because the threads used for various caliber barrels have not been standardized. The thread sizes employed by G. R. Douglas Co. in the past are fairly common so I'll list those below:
  • .32 and .36caliber........9/16 x 18UNC
  • .40 and .45 caliber........5/8x 18 UNC
  • .50, .54 and .62 caliber.. ... 3/4 x 16 UNC
Also, make sure that the width of the breech- plug tang and height of the bolster will match the diameter of the octagon barrel you choose.
The height is most important, the width will fall into place. For those not familiar with the thread notes like "5/8 x 18 UNC" , I' ll try to explain. The "5/8" refers to the diameter of the threaded shaft, or the major diameter of the thread (Figure 2).
Breechplug_Fig2.jpg

The number "18" tells the number of threads per lineal inch. You can have a threaded shaft 12 inches long or 1/2 inch long, but a 5/8 x 18 thread will still have 18 threads per inch. Eighteen threads per inch has a couple of consequences. First, to screw a 5/8 x 18 threaded shaft forward one full inch, the shaft will have to revolve 18 complete revolutions. Second, for each complete revolution, the shaft will move
forward (or back) 1/18 of an inch. A machinist or engineer would say the thread has a pitch of 1/8 inch or about .056 of an inch. This is all simple geometry and you can easily figure similar consequences for any known thread size.

Finally, "UNC" stands for Unified National Coarse. This is a standardized set of thread sizes rec oganized throughout the United States. Unified Nation Fine (UNF) is another common series in this country; and then, of course, metric threads....you can look that up for yourself! Seriously, there's a lot more to know about threads (e.g. class of fit, left hand threads, thread forms), but if you remember that the first number in a common thread note refers to the diameter of the threaded shaft and the second number to the threads per inch, you'll be in good shape.
To breech your barrel, you need to install the plug to fit three sur faces precisely. Most important for the safety of your rifle is the fit of the breechplug face. This must bottom tightly in the threaded portion of the barrel. Any gap there will collect powder fouling, harboring sparks and corrosion. See Figure 3.
Second, at the same time the face of the plug bottoms in the barrel threads, the face of thebolster must screw tightly to the back of the bar rel. Any gap here will be obvious on thefinished gun and detract from its appearance (Figure 3).
Breechplug_Fig3.jpg










 
Last edited:
Stupid question time, just curious if there’s any reason not to file a bit off the upper and lower bolster face instead of filing the barrel surface when fitting?
Im not talking an 1/8”, but more like a barrel flat or two worth of depth.
 
Maybe I missed it..... You will not be able to fully seat a plug with threads that go all the way to the end. Unless some OCD person did the minor diameter in the barrel with a recess-chip relief at the bottom of the hole it won't happen. You'd have to do that with a boring bar in a lathe, nobody does. So, the end of the plug has to account fo the partial threads a the bottom of the hole. I do that with sharpie marker and a file.


plug.jpg
 
Your photo does not show the sholder in the barrel. The plug must seat on the counter bore sholder! Please see figure 3 from National Muzzleloading Association
Larry



Installing a Breechplug | The Apprentice’s Notebook Part 1


Muzzle Loader Building, Muzzleblasts, Muzzle Blasts Archives

The Apprentice’s Notebook​

Installing a Breechplug
By Jay T. Close, Kentucky

INTRODUCTION​

A good measure of your rifle's safety, reliability and durability de pends in how the breech plug is installed. Fitting that plug is not a job to be taken lightly but it is how I usually begin a rifle. If I do a good job here, I can approach the rest of the rifle with confidence that the finished gun will be a safe one. If you're intimidated by this work, some manufacturers -- e.g. the Getz Co. -- sell barrels already breeched. You can be assured of this work. Also, if you buy a barrel and breech plug from Track of the Wolf, they'll install the plug for a modest charge. They too guarantee the work is done right. Nevertheless, the only way to learn to install a breech plug is to fit a few. Moreover, installing a breech plug is a very basic skill, certainly, one required of anyone aspiring to the appellation of "gunsmith". So, buy a barrel and a breech plug to match the barrel threads. You'll minimize frustration if you purchase one of the so-called premium barrels. These have the exterior of the barrel-shaped con centric to the bore and allow you to match the tang of the breech plug to any of the eight flats of the barrel.

GETTING STARTED​

Breechplug_Fig1.jpg

Figure 1 shows a schematic of a common breech plug with its various parts named. When you buy a barrel and breech plug make sure that the threads of the two components match. Be careful here because the threads used for various caliber barrels have not been standardized. The thread sizes employed by G. R. Douglas Co. in the past are fairly common so I'll list those below:
  • .32 and .36caliber........9/16 x 18UNC
  • .40 and .45 caliber........5/8x 18 UNC
  • .50, .54 and .62 caliber.. ... 3/4 x 16 UNC
Also, make sure that the width of the breech- plug tang and height of the bolster will match the diameter of the octagon barrel you choose.
The height is most important, the width will fall into place. For those not familiar with the thread notes like "5/8 x 18 UNC" , I' ll try to explain. The "5/8" refers to the diameter of the threaded shaft, or the major diameter of the thread (Figure 2).
Breechplug_Fig2.jpg

The number "18" tells the number of threads per lineal inch. You can have a threaded shaft 12 inches long or 1/2 inch long, but a 5/8 x 18 thread will still have 18 threads per inch. Eighteen threads per inch has a couple of consequences. First, to screw a 5/8 x 18 threaded shaft forward one full inch, the shaft will have to revolve 18 complete revolutions. Second, for each complete revolution, the shaft will move
forward (or back) 1/18 of an inch. A machinist or engineer would say the thread has a pitch of 1/8 inch or about .056 of an inch. This is all simple geometry and you can easily figure similar consequences for any known thread size.

Finally, "UNC" stands for Unified National Coarse. This is a standardized set of thread sizes rec oganized throughout the United States. Unified Nation Fine (UNF) is another common series in this country; and then, of course, metric threads....you can look that up for yourself! Seriously, there's a lot more to know about threads (e.g. class of fit, left hand threads, thread forms), but if you remember that the first number in a common thread note refers to the diameter of the threaded shaft and the second number to the threads per inch, you'll be in good shape.
To breech your barrel, you need to install the plug to fit three sur faces precisely. Most important for the safety of your rifle is the fit of the breechplug face. This must bottom tightly in the threaded portion of the barrel. Any gap there will collect powder fouling, harboring sparks and corrosion. See Figure 3.
Second, at the same time the face of the plug bottoms in the barrel threads, the face of thebolster must screw tightly to the back of the bar rel. Any gap here will be obvious on thefinished gun and detract from its appearance (Figure 3).
Breechplug_Fig3.jpg










Yes, the plug need to contact the end of the rifling. The unthreaded portion in front of the shoulder at the rear does nothing. Look at them, they are of a minor diameter, smaller than the threaded portion. But I've only built a few hundred, what do I know?
 
Stupid question time, just curious if there’s any reason not to file a bit off the upper and lower bolster face instead of filing the barrel surface when fitting?
Im not talking an 1/8”, but more like a barrel flat or two worth of depth.
I don't recall seeing anyone taking metal from the bolster. The barrel has tons more material to take from. The bolster very little. Maybe a pass or 2 with a file.

One day someone will want/need that plug removed. A bolster with metal removed won't be as strong and could shear off.
 
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