Muzzle loaders would have been proofed under the pre 1855-1868 proof laws I expect for the most part. Some would have been done under 1856-1868 time period. Dont expect many were made after cartridge breech loaders came into fashion and by 1868 they had to by taking over almost all new construction.
Basic black powder proof time frames.
1637- 1855 London black powder.
1817-1855 Birmingham black powder
1856-1868 London and Birmingham black powder
1868-1925 London and Birmingham black powder.
So I guess what I need to find is the black proof levels for a 20 gauge muzzle loader before 1856 and compare it to the cartridge proofs for 20 gauges after 1856 or 1868 if I cant find that. Ive sent an email to the Birmingham Proof house hoping they can tell me. Also I asked what reproof levels they would subject a 20 gauge muzzle loader gun to today, if submitted for reproof.
