Not positive about this "But" I believe that British proof law required a gun to be proofed to at least the minimum of the standard load for the chamber. Thus a higher proof could have been requested by the submitter, but not a lower one. Thus in 12 gauge a 2: proof was standard at 1 1/8 oz, A 2 3/4" one at 1 oz & 3" at 1 oz.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra