I'm of no help Jon regarding 1980 BP proof.
I can tell you that 82 Gr. (3 Drams) of Curtis & Harvey’s No. 4 T.S. (similar but not equivalent to to FFg) with 1 1/8 oz. shot (at 1222 fps) had a breech pressure of 5,820 psi in one report and 6,474 psi in another. Hall & Son No. 4 was similar.
1 1/4 oz. with 3 1/4 Dram No. 4 TS had a breech pressure of 7,790 psi
Definitive Proof under the 1896 Rules of Proof was with 6 1/2 Drams Proof-House Black Powder with 1 2/3 oz. No. 6 shot with a pressure of 10,100 psi.
That same charge of No. 4 TS had a pressure of 16,150 psi.
Those pressures were measured using crushers (LUP) and reported in pounds/ sq. inch; modern piezoelectric transducer pressures would be 10 - 14% higher.
