Another option would be to stay with the drilled touch hole and cone it from the inside. I have found that approach to significantly improve reliability and ignition time while maintaining a small diameter TH.
How is that done?
Since I am dealing with a precarve stock I have little latitude for moving the touch hole. A full chambered breech is not something I would consider.
What I was angling for is the way Hugh Toenjes (Blacksmoke) used to do it. He made a breech plug that was a
little longer. The face was cupped. The liner intersected the cup depression. The liner was screwed into the plug, in the threaded section like CVA.
You get a liner (nice for reliability). You get tidy machining with no exposed plug threads to catch fouling. You get strength. A liner that has a screwdriver slot is very handy in case of a dry ball.
You do not have the long drilled flash hole with a notched plug that can not be cleaned. The plans specify a drilled touch hole of 0.078 to 0.091". That is self priming territory with 2F??
Another thought, I suppose I loose nothing by being HC. I can revise the plug later if I am unhappy with reliability.