The chamber is NOT oblong.

The reason why the brass expands a little more on one side is either gravity or the falling block holding it tightly to the top of the chamber. With the chamber being a little oversized the shell casing sits on the bottom or pushed against the top orf the chamber. When it is fired it has more room to stretch up or down...not sure which way it is stretching...I will mark a case the next time I am at the range and see...


The specs for SAAMI 6mm Remington is .470 my unfired factory ammo measures .466 and my fired brass expands to .474.

So it is a slightly oversized chamber with factory ammo that is undersized(according to SAAMI specs) therefore I get more expansion than I am supposed to.

If I can locate some brass that is actually .470 and neck size after first firing I should be fine....