I've got another explanation that you might want to take a look at, but hopefully this isn't the answer; the chamber is reamed off axis with the bore/barrel. I've seen this before in factory chambered rifles, really badly in one case, involving five (5) separate rifles that came off the same run. These had rifling that extended all the way to the chamber mouth on one side of the barrel. Rotate the bore scope 180 degrees, and the rifling stopped so far up the throat that they looked like Weatherby's with extra freebore. Naturally, the only way any of these were ever going to be tackdrivers was to grab them by the barrel and start using them as a hammer. I doubt, that's the issue here, but I have seen it, and it IS a possibility. Worth taking a look . . .
Kevin Thomas
Lapua USA