Some years back I was lucky enough to come into possession of a secondhand copy of the 1995 Precision Shooting Annual, a compilation of some of the best articles from that year's PS magazine. It contains a fascinating articles by Messrs Ronald A Yerian and Mike Stiverson called Feeding Your Service Rifle setting out Mr Yerian's major problems in loading precision 308 Win ammo for an M1A rifle. Large case-neck and bullet runouts and major shoulder bump variations were only just two of the problems he met and eventually coped with. He finally obtained acceptable shoulder bump consistency through considerable experimentation with makes / examples of sizer die (and returning most as unacceptable) lubes and lube application methods and how he operated the press. It's obvious we start from a much better place today in terms of our equipment and components, but the variations and cures are still relevant.
I summarised these 1990s findings in a feature I wrote a few years back for the Target Shooter online magazine which started as a report on the then new RCBS Summit press but became a three-way comparative review of the Summit, Rockchucker Supreme and Forster Co-Ax each sizing 43 7X57mm cases from three makers some of which had been fired in an old rifle with excess headspace and needed significant shoulder bumps. Maximum amount of bump at the default die setting, range of amounts of bump, and neck runouts / ranges were all measured and compared between the three presses. The die used was an off the shelf Hornady non-bushing FL sizer.
http://www.targetshooter.co.uk/?p=1750
The Co-Ax press was (still is) my personal press so was well used (but mainly on light duty work) and it was up against brand new out of the box examples of the Rockchucker and Summit supplied by the European agent for Alliant ATK which owns Blount / RCBS. As can be seen on the results table at the end of the feature, it can't bump shoulders back as much as the Rockchucker, but produces small variations in the range of shoulder positions. All three produced significantly smaller ranges (0.001-0.002") than the OP is getting and with a much cheaper / lower spec die. (The Rockchucker did best on shoulder position but worst on neck run-outs. It was ergonomically far superior to the other two models in what turned out to be a rather heavier work-session than expected and remains an excellent model for heavy-duty FL sizing.)
I summarised these 1990s findings in a feature I wrote a few years back for the Target Shooter online magazine which started as a report on the then new RCBS Summit press but became a three-way comparative review of the Summit, Rockchucker Supreme and Forster Co-Ax each sizing 43 7X57mm cases from three makers some of which had been fired in an old rifle with excess headspace and needed significant shoulder bumps. Maximum amount of bump at the default die setting, range of amounts of bump, and neck runouts / ranges were all measured and compared between the three presses. The die used was an off the shelf Hornady non-bushing FL sizer.
http://www.targetshooter.co.uk/?p=1750
The Co-Ax press was (still is) my personal press so was well used (but mainly on light duty work) and it was up against brand new out of the box examples of the Rockchucker and Summit supplied by the European agent for Alliant ATK which owns Blount / RCBS. As can be seen on the results table at the end of the feature, it can't bump shoulders back as much as the Rockchucker, but produces small variations in the range of shoulder positions. All three produced significantly smaller ranges (0.001-0.002") than the OP is getting and with a much cheaper / lower spec die. (The Rockchucker did best on shoulder position but worst on neck run-outs. It was ergonomically far superior to the other two models in what turned out to be a rather heavier work-session than expected and remains an excellent model for heavy-duty FL sizing.)
