I would like to see a gun which has failed because of a single pit. Might be able to understand if you were talking about an area of deep pits causing the metal over them to be much thinner and weaker. It is all about location. A small deep pit in the chamber area has more metal over it than it wold just 9" down the bore. Pressure does drop the further down the bore you go but it should still be high at less than 10", I would think.
This would make a good study. Take a gun and bore a hole, with a ED-drill so the hole can be very small, like a pit, at about 9" from the chamber. Load a series of shells to increase pressure from 5,000 psi to 10,000 psi to see if and when it fails. A Crescent would be a good gun to use for this. Decent metal and fairly modern gun should be a good test model.
