[RMc]

Several years ago the Accurate #1 manual listed a number of smokeless loads for the .50-70 cartridge. Since there was no SAMMI pressure standard for this round, a 65 grain charge of FFg black powder was fired behind a 550 grain cast bullet. The 22,500 PSI result was then used as a pressure limit for the 50-70 cartridge. This provided an interesting contrast with the 18,000 PSI SAMMI maximum pressure standard for 50-70's younger cousin, the 45-70 cartridge.

 

[William R. Moore]

There's two issues at work here. Maximum pressure and the pressure/time relationship. IIRC, smokeless has a much steeper pressure curve to peak.

 

[RMc]

There's two issues at work here. Maximum pressure and the pressure/time relationship. IIRC, smokeless has a much steeper pressure curve to peak.

Of that I am aware. Smokeless pressure curves can also be changed with a slower burning rate.