Black Powder Pressures:
3 dram / 82 grains 1 1/8 oz. (1200 fps) is about 5000 psi.
3 3/4 dram GOEX FFFg with 1 1/4 oz. (1240 fps) is about 6000 psi.
4 drams of FFF (about 108 gr) with 1 1/8 oz. (1420 fps) is about 7000 psi.
From
“Powder Pressures At Different Parts of the Gunbarrel, 1895” p. 32
http://books.google.com/books?id=inQ...essure&f=false
(scroll down and click on p. 31)
1855-1925 British Definitive proof for 2 1/2" and 2 5/8" 12g shells - 6 1/2 Drams BP with 1 2/3 oz. No. 6 shot = 4 1/2 Long Tons or about 14,000 psi by LUP or about 15,000 psi by modern piezo transducers.
1925-1954 British Definitive Proof for 2 3/4" 12g shells - 7 1/2 Drams FFFg with 2 oz. shot. Mean pressure to be developed by the proof load was 7.1 tons LUP / 15,900 psi with a maximum of 7.8 tons / 17,500 psi.