Looks like the ol' 'wrong guage' and 'obstructed bore' problem. Although this may resemble classical Darwinism in operation... it is really, really easy to do. Be on your toes when you are at the range and the guys are all swapping guns and magazines willy-nilly. If there is a noob in the mix, the possibility of something like this happening goes through the roof. It happened to me years ago when I spotted one of the kids on the line trying to put a magful of .38 Super into my .45 Colt. The only reason I caught it was that the mag was stainless steel, and at the time all my mags were anodized or blued black. We shut down the line, dropped the curtain - and sorted out our guns and mags and checked our bores.