And use the correct datum point diameter...the closer to the body gets bumped less than the datum point in the middle of the shoulder. The 10mm case, disregarding whether the mouth is truely square and is getting centered up on the shoulder to begin with, would be measuring too far toward the body. The "10mm datum point" could be getting worked 0.003", but the true datum point is getting set back farther and defeating the purpose you are striving toward.
It is not a HUGE amount more, but it matters. I was using the 400 bushing to begin with and then realized I should have been using the 350. Had to reset my sizing die after using the correct bushing.
And thanks to THIS SITE and its GREAT POSTERS for turning me onto the headspace tool because setting up my dies like I always had been show was giving me bump back like the OP and I was getting separating brass on the third firings!!
It is not a HUGE amount more, but it matters. I was using the 400 bushing to begin with and then realized I should have been using the 350. Had to reset my sizing die after using the correct bushing.
And thanks to THIS SITE and its GREAT POSTERS for turning me onto the headspace tool because setting up my dies like I always had been show was giving me bump back like the OP and I was getting separating brass on the third firings!!