Somewhere in my files I have correspondence from someone who bought a 12ga Elsie, Damascus barrels, 2 3/4" chambers. His club wouldn't let him use the gun at their facility. He had it sent to the UK, got it back, passed CIP "standard" proof (850 bar). What shells to use in the gun? The Brits said any standard 12ga load--which, to them, means "standard proof", NOT superior or magnum proof. I pointed out to the individual that SAAMI service pressure for the 12ga is 11,500 psi, while CIP standard service pressure is 10,730 psi--so he likely would not want to use typical US 12ga loads in that gun. But especially with 2 3/4" chambers, it'd be very easy to work up loads well under the CIP standard service pressure limit.
We're still not quite speaking the same language as our British cousins when it comes to certain topics (like pressure). But if we take the time to understand what they're saying, we can safely use their guns (and our own vintage guns) with modern ammunition. Either British/European, RST, or our own reloads.
