If you're going to spend a few hundred dollars with a gun smith to reprofile, cut, and alter your barrel to fit in a $75 gun bag, wouldn't it make sense to buy another bag.
Is 1mm worth the ass pain that the ATF could bring down if you shaved too much off?
Would anyone ever find out? Probably not, but why take the chance.
I had the same argument with a gun smith in Tallahassee, FL when he returned my 14.5" Heavy Barrel w/ a 1" A2 birdcage on it. Needless to say, it was the last time I ever gave him business. He even had the audacity to attempt and charge me more money for him to go and re-do the work.

