If the drum threaded hole doesn't allow for a switch to a liner that will leave the flash hole in the right position for you,,
I would do the following:
If the drum threads are deep and strong I would use those if possible and a liner with a shallow counterbore.
If they don't look to good, I would recut the threaded hole one size larger and re-tap with a fine thread.
If you do the latter you can also reposition the drum threaded hole just a little as well.
Recutting/tapping the hole,,then cut a shallow counter bore at the entrance to eliminate the flush surface start of the threads.
Then make a replacement liner Blank (no flash hole yet) threaded to fit that new hole and with the small counter bore rim on it. Leave it long enough to hold on to for installation.
**Make this from plain carbon steel...not stainless. You want this to 'hide' once it's installed and the area of the bbl has it's finish touched up. No sign of a Liner,,just a flash hole in the right position.
Run it in tight, Cut it off just above the surface of the bbl flat on the outside and trim down. Just before the thing is flush, rivit the edge of the new liner into the counterbore around the edges. Don't hit the bbl flat, just the very edge of the new vent liner. I use a small punch and hammer.
The soft steel(s) will cold fuse together and when the blank plug liner is finished off, it will not be seen if done right.
Usually the difference in steel alloy color shade when finished and polished will give it away. But rust browning or rust blue it when completed will make that go away.
I wouldn't use LockTite of any such things to secure it, Just a very tight instal.
If locktite or something like it is used and it gets in that counterbore area, it will sieze there and show a very thin but distinct dark ring when polished flush.
Installed tight, it isn't going anywhere. No body glues the percussion drum in place with the notion that it may just come loose at some point. Not unless the install was less than satisfactory or it's loose in it's clocked position to begin with.
On the inside, file the new liner to conform to the bore.
Now you have a new blank bbl flat to place the flash hole where it needs to be and no evidence of it's past.
Once the new F/Lock is in place, mark carefully and drill for the new vent hole.
If you prefer the Coned vent, cut it from the inside with the handy home-made coning tool as seen on these pages.
Made with a Demel HS steel V point cutter and a simple handle and extension.
They cut evenly and quickly. Cheap to make too and last and last.
Maybe you don't want or need it coned like a Lightn'in Vent Plug.
Just a straight vent worked OK too for many centurys as I understand it.
Anyway,,That's what I would do
