Why are shotguns listed as "proofed" for 1 & 1/4 ounce loads? Couldn't the pressure vary considerably between two different loads, or am I missing something. I suppose this is a pretty basic question, and I never really cared when I just had a 870 Wingmaster. Bur I find my interest taking me to the doubles these days and want to understand everything I can about them.
Thanks for the help, and patience.
Gary