Breech Plug trouble

[Ryan Saunders]

I've run into a problem. My breech plug will not screw all the way into the barrel. It will go up to about 1/8" from being right. What should I do?

 

[Zonie]

The threads on your breech plug run all of the way up to the face of the plug.

The threads in the barrel stop short of the shoulder where the threads end and the bore starts.

Use a flat file to carefully file off the first two (or so) threads.

To do this, without the plug in the vise I usually close the jaws until the gap is less than the thread diameter. I can then lay the threads of the plug in the gap to support it while I'm filing.

It's a good idea to warp a piece of masking tape around the threads leaving about 1/8" of the threads exposed because the tape will help to protect the threads which you don't want to file.

When filing, you only want to remove the threads, leaving just a trace of the bottom (root) of the thread on the outside of the plug.

After removing the two (or so) threads try the plug. I'm betting it screws in until the face of the plug bottoms out on the shoulder down at the bottom. If it doesn't, you might have to remove a little of the third thread but usually just removing two will do the job.

 

[Ryan Saunders]

That's what I was thinking I might have to do, I just wasn't sure... it seems like that might fix the problem with the barrel maker stamp winding up on the top flat too. I might go ahead and try that... it's the only option really I guess. It seems like they would make the breech plug to screw up plumb with the barrel though without any filing. Oh well lol

 

[Zonie]

The other, much more expensive option is to buy a bottoming tap that can cut full threads all of the way down to its end.

These are sometimes rather hard to find so if you have a 6" bench grinder you can buy a plug tap and slowly (using lots of water to keep the tap cool) grind the end back to remove the partial threads at the front.
In the sizes used for breech plugs, this can also be a fairly expensive proposition.

As for the barrel makers marks being on the top flat, the odds are 7 to 1 in your favor of them being elsewhere. :grin:

I guess in all fairness, if the makers marks are on the top flat you can file the face of the breechplug and the two shoulders where the tang is back to allow the breech plug to rotate further into the barrel. This will in essence cause the tang on the plug to line up with the next flat.

Removing only .008 from these surfaces will rotate the plug one barrel flat if the threads are 16 per inch.

 

[Ryan Saunders]

Ok, I'll go have another look at 'er and see what I can do. Thanks

 

[Ryan Saunders]

Well, I took it down three threads I think, and it came out right so it's been a good day lol. I also managed to get the tang and then the lock inlet completely by about 10:30 tonight, so I'm gonna hit the sack and start on the trigger tomorrow.:hatsoff:

 

[MSW]

NMC- glad to see that you got it solved ... Zonie's right (he almost always runs that way) ... the whole trick to building is to go slow. i didn't realize this at first, and messed up a bunch of parts, including a breechplug, 'cause i got all enthusiastic and took off way too much. Now i use a finer file and a lighter touch on it.

Good luck with your build!

 

[Ryan Saunders]

Thanks! :grin:

 

[Vaino]

Evidently w/ the bbl maker's name ending up on the top flat, you're fitting the Bplug from scratch. First off, I'd take a bottoming tap and make sure the threads go to the ctbore flat and then start on the plug threads. A word of caution...some bbls that are .54 cal have 5/8-18 threads and don't have a lot of land to shut off on and removing threads could eliminate any chance of a shutoff. Also depending on the Bplug,sometimes there's a large fillet or radius at the junction of the plug and bolster and either this radius has to be reduced or the bbl ctsk has to be increased or possibly the plug isn't threaded all the way to the bolster and the bbl ctsk again has to be increased or a thread die would has to be used. Good luck.....Fred

 

[jhenry1728]

If you're doing a touchhole liner, make sure everything clears the face of the breech.