The key words are "substantially" reducing the strength of the barrel as fitting a multi choke boring out to cylinder dose not effect the overall integral strength of a barrel .British proof can be a mine field ,even those of us that are involved with regularly submitting guns get confused with 8[?] changes in proof law and stamps in the last 100 years .No wonder we can not keep up .Personally I think its time we started from scratch again ,but that's not going to happen so we just muddle along as best we can hopping we get it right most of the time.
