Are we talking about two proof loads or double proof loads? If a regular proof load is, say, 150% of normal operating pressure, then double proof load would be 300% of normal load or about 30,000 psi which is the pressure that both steel and Damascus Parkers blew in the Sherman Bell tests. Any pressure proof is fine if a gun is designed for it. I cannot imagine that the proof house arbitrarily doubled the proof amount. I can also not imagine that their proof load would differ from Birmingham. But then, I also cannot imagine a new Purdey blowing.

Some facts are definitely missing. I wonder if the proof house has been asked about the brewing controversy.