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Old March 26, 2009, 07:28 AM   #6
Bart B.
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Join Date: February 15, 2009
Posts: 7,283
I've got an RCBS Jr. and two Rockchuckers. Each one has some spring to it. 'Tis the nature of those things. How much can be measured with a dial indicator. It varies with the type of lube, how much lube's on the case, how thick the case walls are, and the difference between fired case and internal dimensions of the die.

The slightest amount of lube results in shoulders being set back very little; the press will spring quite a bit. With more lube, shoulder setback is more as the press springs less.

Each of my several .308 Win. RCBS full length sizing dies will have different clearances between their bottom and the shell holders to size cases to a given case headspace. This was verified by putting a chamber head space gage in them and measuring the difference between gage head and the bottom of the die. These dies also vary a couple thousandths in body diameters so the smaller ones size case bodies a bit more than the larger ones.

I've put each one in the press, put my .308 Win. "go" gage (1.630-in.) in the shell holder, raised the ram then screwed the die down to just stop with its shoulder against the head space gage shoulder, locking it in place. Each die has a different gap beteen its bottom and the shell holder. All cases sized with this set up have longer headspace than the gage by some amount; proof that there's some spring in the press.

I tumbled my deprimed and cleaned brass in a foam lined can coated with thin film of lube. This way, all the cases have a narrow range of sized headspace; typically .002-in. Every time I've tried rolling cases on a lube pad or other such surface, the amount of lube varies so much across the cases that they'll have a lot more spread in headspace. Cases sized too much with too short of headspace typically didn't shoot as accurate. And, of course, way too much lube will dimple the shoulder.

Another interesting thing I've noticed is case weight can effect their sizing for a given setting of the die in the press. Sizing WCC-58 commercial cases weighing 150 grains, those thin cases will have a lot of shoulder set back for a given amount of lube on them. In contrast, really heavy cases such as M118 or M852 match ones weighing 30 to 40 grains more don't get as much shoulder set back sized the same way.

Last edited by Bart B.; March 26, 2009 at 07:56 AM.
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