RE: Green mt. barrel hang fires?
Idle curiosity Q fer ya, does the breech plug have a *clean out port* in the side or is it a solid casting?
Iffen it has a clean out, pull the plug and do a MAJOR cleaning number from the port to the breech (inside the barrel) using the pipe cleaners with the nylon bristles or yer preferred method. Secondarily look for burrs in said port that *may* be causing a delay of the cap spark to the powder.
Frankly Ive had my own brand of hassles with some of the breech plug casters and usually end up redoing the breech to a Nock style geometry (bell shaped main area plus opening up the port to the nipple a bit more via grinding, etc.) when I build my rifles. Sorta "blueprinting" the breech plug as it were.
Of note is that with this type of work to the breech plug in conjunction with a lock tuning one can get some mighty fast reaction times out of rock locks this way (comparable to side hammer cap locks)
Keep yer powder dry,
D.