breech plug seal

[knifemaker3]

Hey all,
Got a question.  I'm working on putting a new barrel on a commercially made percussion gun.  I'm going to have to make my own breech plug which will be made from a grade 8 bolt. 

My question is how closely should I match the face of the breech plug to the hole?  I purchased an Oregon barrel pre drilled and tapped.  I have ran my bottoming tap in as far as the shoulders of the drilled hole to extend the threads as far as possible.  Should I match the angle in the bottom of the hole with the face of the breech plug or will it be ok to leave it squared?

I'm used to working on modern guns but haven't done much with muzzle stuffers henchforth the dumb question.

Thanks

[Daryl]

Makes sense to me. A non-matched breech face will leave a gap for fouling to collect- and stay, especially if you don't remove the barrel for flush cleaning.

[knifemaker3]

I reached in with a boring bar and made the bottom of the hole flat to match the flat face on the breech plug.

Now I have another question.  In order to match the lock on the rifle the drum hole is located to where the breechplug will extend past the hole.  I want the drum to fit just in front of the plug.  To do this I will have to shorten the breech of the barrel and the plug.  How many threads will be safe to have when I shorten this area up?  What is the minimum depth you can have for depth of breechplug?

Or, should I bore out the breechplug enough to allow the powder to go into it and install the drum so it matches the preexisting stock and call it done?

[thimble rig]

Modern breech plugs the length is 1/2 inch long.