The resident gunsmith, Willie Boitnott, during the NMLRA National Matches during the '80s at friendship, IN, used tiny round mirrors, which were highly polished pieces of polished steel, as I recall. He would drop one the right size down the bore until it rested on the breech, then shine a light down the bore and view it. I got him to check the bores on a 16 bore Powell for me, in about 1985, before buying it.

The above method of dropping a tiny flashlight down against the breech will not allow you to view the very bottom of the chamber area, which in many cases is the most deteriorated area of a muzzleloader bore. The length of the flashlight area of the breech cannot be seen.

SRH

May God bless America and those who defend her.