Per Vic Venters' book "Gun Craft", quoting former proofmaster Roger Lees, who held that position when the 1954 Rules were adopted, referring to those new rules: "in general it may be said that under the new Rules of Proof no arm will receive a more severe proof than hitherto. Some such as the 12 bore 2 inch and 4 and 8 bore guns, will now receive a less severe proof than they received heretofore." I thought I recalled that the Brits went to a less severe proof for the 2" 12, as requested by makers of those guns, under the 1954 rules of proof. I think that continues to the present.
Confusion here, where 2" 12s are concerned, may stem from the fact that when the Spanish made their 2" 12s, they submitted them for 850 bar proof, just like standard 2 1/2" 12s. Which explains why Brit 2" 12s are typically quite a bit lighter than Spanish 2" 12s.
