It is interesting to note I have a twist bbl'd Lefever H on which a "Flaw" could be seen with the unaided eye. At 14"s from the breech on the left bbl tha appearence was that it had been struck on a sharp cornered object & dented in. It had then apparently been fired, resulting in a crack about ¼" long following a weld seam. One side of the crack was still dented in & the other side had lifted leaving an opening one could look through to the opposite side of the bore. This gun had been bought very cheaply as a parts gun & the bores were "Baddly Pitted". I subsequently put my expanding dent plug under the break & raised the part which was dented in & hammered down the raised flap, till one had to look very closely to see the crack. It was then placed in the "Firestone Proof Chamber" & several factory 3¼de-1 1/8oz loads fired with no visable results. Then several more 3 3/4-1¼oz factory "High Brass Express" loads fired with identical results. Finally several more handloaded shells using a lower velocity loading of 1 3/8oz shot were fired. It still sets in my rack today & one now has to use a magnifier to even find this crack. Now I realize some of those "Hidden Flaws" which cannot be seen may be miles worse than was this one with daylight shining all the way through, seems sorta doubtful though, doesn't it?? Also this flaw was not in the High pressure chamber area, "BUT" for how many years were we told that was where the dangerous area for a damascus/twist bbl bursting was, right out there where your forward hand was. I didn't then & am not going to now, because I Know for a Fact this bbl is cracked, but all those shots I fired through it "Could" have been fired from a normal shooting position & I would still have both hands & all of my fingers.
