ya I would think after 50k the rifling was all but gone and if anything pressure would have dropped because of it. About like shooting a 401 bullet out of your 41 mag. Either it was fatiqued metal or a bore obstruction. Keep in mind that guns are proofed at over double operating pressures so I doubt unless the guy was mistaking pistol powder for rifle powder youd get enough of an overload to do that. Using most powders that are handload in a 308 there isn't enough case space left to double the pressure. Might get a sticky or stuck bolt or a pierced primer but to actually rip a barrel open your talking LOTS of pressure.