Under our SAAMI standards, 12ga maximum average pressure is 11,500 psi. That's higher than I'd want to go with a Damascus barreled gun. Assuming it has 2 1/2" chambers as does your French gun, the extra length of a 2 3/4" hull will increase that pressure somewhat. The average increase in Sherman Bell's tests reported in Double Gun Journal was a bit over 700 psi. So now you're on the far side of 12,000 psi. I think most people who reload 2 3/4" hulls for use in Damascus guns with 2 1/2" chambers would advise you to steer clear of pressures in that range. American shotshell manufacturers focus on producing loads that meet the stated velocity (which gives some idea of how much recoil they'll deliver), but only concern themselves with SAAMI pressure standards.
