According to A Baron Englehardt, charts in his gun digest article on proof 1887 proof rules for the 2½" 16ga called for 10 3/4 drams powder under a 399 grain round ball for provisonal proof, 5½ drams powder under 1 1/3oz shot for definitive proof & the service load was 2 3/4 drams powder under 1oz shot. By 1925 this was changed to 8¼ drams with 1oz shot for provisional, 5 3/8drams & 1½oz shot for definitive with the service load the same. These were of course for the Black Powder proofs. For the service load it was noted "Black powder or equivalent in smokeless".
These proof charges would seem to exceed the normal, perhaps some type of "Enhanced" proof of which the maker was proud & had it stamped on the bbls.
