We are all fortunate indeed that the makers of a century+ ago didn't have to wait on Bell. As smokeless powders came into general use they simply insured their guns had adequate thickness in the "Breeches" & guaranteed them for smokeless. I truly wonder where they found this out.
By the early 1920's of course E I DuPont De Nemoures Had those pressure curves well drawn out, but the Gunmakers practise of wall thickness proportions had by then long since been established.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra