The "Rodman Gun" was used during the civil war.

I can well imagine he needed to control the burn rate of black powder. It was an 80-ton cannon, the largest in the world at the time.



While pressure guns may well have been around for a long time, I think the question still remains, "When did pressure supersede loads for proof house standards?"
Certainly into the mid 1920's proof was done by load.

Pete