Well I've been in communication with the Birmingham Proof House as well as a gunsmith friend and here is some of the preliminary info. I'm still waiting on some clarification from BPH, they have a whole manual of specs based on gun type etc. I'm trying to get the specifics for black powder guns.

The gunsmith friend suggests that there should be no change in dimentions in the area of and nearthe chamber. He also noted that a change of 1 or 2 thousanths probably would still be safe but would prefer no change. He also said that the nipple would most likely blow out before the barrel would bulge, at least that's what he has seen when people have brought in guns that were over loaded or shot with smokeless loads. In his experience, a barrel is much more likely to fail from short starting the projectile than from overcharging the barrel. This of course is not an endorsment to overload a barrel, always follow the manufacturers load recomendations.

Still waiting on other sources of infomation and will post it when it arrives.

Have a good day.