I've had forcing cones lengthened on several guns. The only difference ever noted on paper or on the shoulder was my 3 1/2" 10, which had factory cones cut short and slightly off-center. On the pattern board, two ounce bismuth handloads gained percentage points at 60 yards with improved eveness, possibly from fewer broken pellets. No scientific tests but it did seem to make the heavy recoil more of a push than a slap. If the loads lost velocity it didn't matter with the large pellets (BB).