Yeah, the factory dimensions can be all over the place, especially in older rounds, and particularly European cartridges. My 6.5x55 is chambered with a minimal PT&G reamer, and so far NO American brass will enter the chamber unless the rear end is sized down, but Lapua brass is perfect. Limiting myself to Lapua brass is no biggie.
Have also owned an FN commercial Mauser that had such a short throat some American "enhanced velocity" factory loads blew primers--and got over 3000 fps from the 22" barrel. Have also seen custom chambers for Weatherby cartridges that blew primers on the first shot with factory ammo.
All sorts of stuff happens if we vary chamber and bore dimensions.
