Popular wisdom what is your reputable source for this fact?

While some may throw out a number, it is a throw not necessarily a fact based on testing. This why there is a proof house to provide some reliable basis for judgement.

While 0.025 is on the low end, as others have already noted it depends on where. My father and I have put more than a thousand shells (custom low pressure sub 6k) through a pair of Damascus barrels barrels which are below 0.030.

Michael Dittamo
Topeka, KS