Black and Nitro powder Service and Proof Charge Pressures
https://books.google.com/books?id=inQCAAAAYAAJ&pg=PA296&dqExperiments to ascertain the pressures given by service charge and proof charges used in England have been carried out by The Field. Under the existing Regulations of Proof in England, a “service charge” is specified for every bore, and the compulsory definitive proof is made with double the service charge of proof-house powder and 1 1/3 (times) the service charge of No. 6 shot. Besides the compulsory proof, a supplementary proof with other kinds of powder is permitted, if applied for. Many other charges, both larger and smaller than the officially stated “service charge”, are in constant use.
Curtis & Harvey T.S. (Treble Strength) No. 6 was coarse Black Powder somewhat similar (but not equivalent) to Fg; No. 4 medium, FFg; No. 2 fine, FFFg.
https://books.google.com/books?id=mFcCAAAAYAAJ&pg=PA271&lpg “S.S.” (Smokeless Shot-gun) was a Bulk Smokeless powder made by Smokeless Powder Co. It was discarded as loading with higher charges of powder produced significantly greater pressures than “E.C.” or “Schultze”.
Pressures were measured using crushers (LUP) reported in pounds/ sq. inch and
modern piezoelectric transducer pressures would be 10 - 14% higher.12 bore
Nitro 1 1/8 oz. with 42 grain Bulk Smokeless = 3 Dr. Eq. (1200 fps): 5330 - 6110 psi
Nitro 1 1/4 oz. with 45 grain = 3 1/4 Dr. Eq. (1220 fps): 6360 - 8620 psi
16 bore
Service charge 1 oz. 2 3/4 Dram Eq. = 38 gr. Bulk Nitro powder.
C&H No. 4 - 7,480; “Schultze” - 8,250 psi; “E.C.” - 8,960 psi
20 bore
Service charge 7/8 oz. 2 1/2 Dr. EQ. = 34 gr. Bulk Nitro powder
C&H No. 4 - 8,240; “Schultze” - 8,220 psi; “E.C.” - 9,100 psi
