Breech Plug Question for the Doctors

[Gtek]

I picked up a never used tanged percussion breech plug a while back 1" 5/8"x18 2 1/2" tang and the "Offshore" chamber is right at .265". Been sitting on my desk for a while periodically taunting me as to the direction it goes. Other night I remove finger tight nipple and look into holes with flashlight and flame hole is about 85% blocked under nipple, hummmm? Looked at it really well with magnification and you can see the circle location through flushing on side surface on exterior of a pin or screw covering flame hole drill. Not being able to see any threads on internal protrusion my head starts leaning to machine tools in garage.
Questions- Would you drill/clean out whatever and tap for a set screw custom fitted correctly timed angled tip to create a now you know for sure? Also would you open up the Offshore chamber some for maybe a better everything.
Thanks, Lar---

[waksupi]

Considering it is a cheap part even if you screw up, I would definitely enlarge the chamber. I'd skip the set screw, drill and tap, and file on the contact surface of the drum to properly index.

[rfd]

There are at least a few variations of the patent breech. Most patent breech plugs screw into the barrel proper, and where they stop is the beginning of the real chamber. The threaded part of these plugs incorporate their ante-chamber and drilling out that hole to any significant degree may create an unsafe condition.

https://i.imgur.com/Bm0j02b.jpg

[rfd]

GPR type patent breech plug, flinter ...

https://i.imgur.com/YQPBcqx.jpg

... plug and barrel view at the chamber end ...

https://i.imgur.com/xPJEa42.jpg

... make sure to anti-seize grease the threads!!

[Gtek]

Great information, pictures and drawings and Thank you gentleman for your time/thoughts. It is (kind of) similar in design to a TC on the side, thread is undercut at base to about .520" x .100" and was a little leery about opening ID so maybe a just a good polish there. The external flushed pin/screw into flash hole is the how to fix issue, go through nipple hole and clean out and let her eat or drill remove and go threaded plug. Was leaning into probably a 36 or a 40 then post index mill breech to barrel measurement.

[waksupi]

My thinking on it is the barrel itself would take care of any extra pressure, which I think would be negligible.