Raimey;
What would that 2.6Gr BL represent. Understand I am not disagreeing with your interpretation of 2.6 Grams Lead, but this doesn't really seem to be a plausable marking. 2.6 grams would equal about 40 grains or about the wt of a .22 LR bullet, certainly not one for a 9.3mm caliber, or the shot wt for a 16ga.
My old busted up 1907 16/16/8x58R Sauer drilling with nitro proofs has the shot bbls marked 2Gr Sch P & 28.3 BL. This is a light powder charge of slightly less than 2¼ dram with 1oz shot.
The 2.5Gr Schultz on this one would equal to a load of 2 3/4 drams, but what would one do with 3/32oz of shot. None of the pics are coming through on my old dial-up except the last one, but surely this is an incomplete stamp. Is it on the rifle bbl or the shot bbls. If the rifle bbl & "IF" it were 12.6 Gr Bl it could denote about a 195 grain lead bullet which would be reasonable for an early 9.3x72R. Sometimes this is marked as Bl G ,Bleigeschoss, or lead bullet. A lead bullet of about this wt ahead of about 32½ grains (2.1Grams) of the flake rifle powder would sound right for an early 9.3x72R.
