I don't know if it was reproffed at 2 3/4 or just restamped to look like it was. Maybe our British board members can tell us. Clearly it looks like it was proofed at 2 1/2" and it clearly reads 2 3/4" now. Were 2 1/2" guns proofed at 3 1/4 tons or just 2 3/4" guns? Either way CIP loads should be the max used in this gun. Some of the reloads Skeet and Sporting Clay shooters load will be above those proof loads.