Thanks to all for the education, time and insight.
I think I am learning enough now to be dangerous. If someone has the time please review below and let me know if I am getting a little brighter on understanding this can of worms.
On a very simplistic basis - it is very difficult to accurately convert british proofs to PSI, because the U.S. and England (proof houses) use different standards for measuring pressure. It sounds like there are some conversion factors that some of you feel are reasonably accurate (I haven't digested if they are essentially the same)
If you have a 2 1/2" chambered 12 ga gun that is proofed for:
Nitro Proof for 1 1/8 oz (proof mark for 1904 to 1924?)
3 tons (proof mark for 1924 to 1985 or so?), or
850 BAR (post 1985 or so) ALL THREE BEING ABOUT THE SAME PRESSURE TEST - THEN KEEP SHELL PRESSURE BELOW 8500 - some felt 9000. To do this you need to use CIP, Poly Wad or RST shells. Fortunately that is all I have ever used.
Question - if a 16 ga gun has proof marks for 1oz Nitro Proof and 3 tons it was probably also reproofed? Again use above shell selection.
It seems like the guage would impact pressure, and a 16 ga at 3 tons and a 12 ga at 3 tons would need to take different pressures, or the 16 ga would need thicker or stronger barrels?
Pressure does not equal recoil, because recoil is measured in foot pounds.
U.S. manufacturers are not as concerned with pressure because they are trying to meet a different standard i.e. FPS, and change powders from time to time resulting in different pressures, but the same FPS.
Depending on the age of your English gun and proof, there could be times that some standard U.S. ammo might work - at lease based on tests run by Amburst for 16 ga site.
It sounds like there is a mimimum standard the Brits are trying to meet for all guns. For that matter same goes for U.S. guns, and maybe guns imported for use in U.S.?
