W W Greener shows the 1904 proof charges in his 9th Edition of The Gun.
Black powder proof for 20 gauge was
Provisional = 205 grains TSP (7 drams) with 7/8oz shot (383 grains
Definitive = 136 grains TSP (5 drams) with 1 3/16 oz shot (520 grains)
Service = 68 grains (2 drams) with 383 grains shot (7/8oz)
Supplemental proof for guns to be used with Smokeless Powder
95 grains (3 drams) TS2 with 574 grains shot (1 5/16 oz)
Service only lists 7/8 oz of shot, no powder charge stated so assumed to be same 2 dram equivalent.
Almost identical to the 1954 rules half a century later. The only difference I note is the 1 3/16 oz shot charge in definitive proof in 1904 versus the 1 5/16 oz in 1954.
No chamber length is given in these 1904 rules so apparently the same for all lengths.
