As an amplification -
Suppose a well-heeled man places an order with (insert favorite custom shotgun maker here).
They ask him which load he wants the gun to be regulated with.
Seriously, they do. If they forget to ask, the customer should tell them. He should fully expect that for his (insert vast sum here) and several year wait that the gun should shoot as specified.
Now, suppose the load chosen was the classic 1 1/16 oz. 1250 fps Eley Grand Prix.
Should our sport now choose to warm up for the season with the ever popular 7/8 oz. hand load that the books all run at 1300 fps he should not be shocked when the gun cross fires a good bit.
When stuffed with a 1 1/4 oz. load running at a lower velocity, say 1125 fps, to 'tame recoil' that gun will spread fire, ie the right barrel will shoot to the right. Guaranteed.
Bore time trumps mass of ejecta. A heavier bullet will cause a pistol to shoot higher.
So, field guns that crossfire with target loads are not necessarily built wrong. Neither are trap guns that throw duck loads off to the side.
