Options for indexing a breech plug ?

[Sudsy]

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.

 

[waksupi]

I would shorten the plug, plenty of thread will be left.

 

[Sudsy]

This is my first from scratch build.

What is considered the minimum amount of thread ?

 

[Flintfan69]

.

 

[64Springer]

With respect, if you need to ask how to perform this very simple operation, find a professional to do it.

 

[Phil Coffins]

Never use a shim at either end, start by making the barrel threads as close to the end of the bore with a clean square corner. Then match the plug to that with the plug sealing the bore, and, the tang indexing to the flat.

 

[Larry (Omaha)]

I would shorten the plug, plenty of thread will be left.

"Picked up a .45 rifled pistol barrel and plug. The threads in the barrel end about 1/4" before the plug is fully seated."
As stated by the poster above the plug would not seat on the counter bore shelf. The plug can't go in because there is no threads. Cutting off the plug will make it too short to seat. Phil is spot on.
Larry

 

[Sudsy]

With respect, if you need to ask how to perform this very simple operation, find a professional to do it.

Absolutely !
I don't have the equipment to do this anyway - But at the same time I'd like to know what the proper way is to do it. When I ask the "professional" how he's going to do it I want to get the answer that tells me he's going to do it the right way.

 

[64Springer]

Absolutely !
I don't have the equipment to do this anyway - But at the same time I'd like to know what the proper way is to do it. When I ask the "professional" how he's going to do it I want to get the answer that tells me he's going to do it the right way.

There are retail muzzleloading shops that will fit that plug for you.

That way you'll be assured that it's being done correctly.

I wouldn't take it to joe blows machine shop in the hopes that the shop can figure it out.

And thank you for not taking offence. We all have different aptitudes when it comes to performing certain tasks.

 

[Sudsy]

And thank you for not taking offence. We all have different aptitudes when it comes to performing certain tasks.

No problem and not even a little bit of offense.

I can handle the woodwork and carving, been doing that for 50 years, since I was a kid - the machining stuff not at all.
I'll blow myself up for sure, so I'm not afraid to ask the dumb question rather that risk the dumb mistake.

 

[waksupi]

"Picked up a .45 rifled pistol barrel and plug. The threads in the barrel end about 1/4" before the plug is fully seated."
As stated by the poster above the plug would not seat on the counter bore shelf. The plug can't go in because there is no threads. Cutting off the plug will make it too short to seat. Phil is spot on.
Larry

If the picture shows the plug turned in as far as possible, cutting off the plug is still the solution. Any threading to a depth over the diameter of the bore is excess.

 

[Sudsy]

Any threading to a depth over the diameter of the bore is excess.

Thank you, I'll remember that

 

[Larry (Omaha)]

If the picture shows the plug turned in as far as possible, cutting off the plug is still the solution. Any threading to a depth over the diameter of the bore is excess.

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
Larry

 

[SDSmlf]

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

The basic concept of indexing a breech plug is simple in theory. Execution, not so simple. You want the end of the threaded plug to be tight against the shoulder or step in the bore, while the faces of the barrel and breech plug come together tight. If the threaded plug is too long, you cut it back. If the end of the threaded plug isn’t getting to the shoulder in the bore (too short), cut the barrel back.

‘Simple’ with a lathe at your disposal, doable with files….. No insult intended, but based on your OP, likely well above your current pay grade and skill level. Places like TOW used to charge $25 I believe to fit a plug when you purchased a barrel and plug from them. Others offer similar services. You are likely to pay more for shipping both ways than cost of the service. Many scratch builders start with breeched barrels.

And if you are a 1/4” away from seating, with an 18 TPI pitch for example, you are 4-1/2 revolutions from seating. Without a lathe, a lot of precision filing.

Hire this one out. If you must, get hold of some practice pieces and practice. Don’t get into an endless loop on your first scratch build.

 

[Dartwick]

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

I think you misread the OP(or maybe I did.)

I think the OP is saying the the plug threads are hitting the bore before the tang face hits the back of the barrel.

My first though it put some inletting color on the front of the plug and turn it in, take it out, and make sure you see color on the shoulder at the bore - before you start cutting and filing.

 

[Larry (Omaha)]

I think you misread the OP(or maybe I did.)

I think the OP is saying the the plug threads are hitting the bore before the tang face hits the back of the barrel.

My first though it put some inletting color on the front of the plug and turn it in, take it out, and make sure you see color on the shoulder at the bore - before you start cutting and filing.

From the OP
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?
Larry

 

[Whiteoak15]

A salvage machinist at a large machine shop told me that usually a minimum amount of three full threads is required to meet the design criteria for holding a load. The more the better, but a minimum of three. Also, I would use some never-seize on the threads when I installed the plug.

 

[Dartwick]

From the OP
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?
Larry

I think you have a mental block or something. Or maybe your not following his literal layman's explanation of whats happening.

Hes saying he would need 1/4" more threads in the barrrel in order to have the face of the tange and the back of the barrel kiss.

Look at his picture.

 

[Rebel bull]

This is my first from scratch build.

What is considered the minimum amount of thread ?

as a retired mechanic/machinist the rule of thumb is 1 diameter long. but....... before you start cutting you need to be absolutely certain that you have a flat bottomed hole ie; full threads to the shoulder and the plug has to be square then trim the plug until it clocks correctly

 

[Comfortably_Numb]

Absolutely !
I don't have the equipment to do this anyway - But at the same time I'd like to know what the proper way is to do it. When I ask the "professional" how he's going to do it I want to get the answer that tells me he's going to do it the right way.

You don't have a file?