I bought a 10 Short Action with a 4.27 screw spacing. I wanted to build a budget target rifle. I installed a Shaw .308 Varmint barrel. I set the headspace at a minimum. Virgin brass and unfired .308 rounds chamber perfectly. Some of the brass I sized, like 10% of it, chamber perfectly or with a slightly tight bolt. The rest won't chamber at all.
Setting the Die: I use a Dillon 550. I screwed the die down until it contacted the ram, then backed the ram down and turned the die another 1/8 to 1/4 turn, so that the ram actually cams over when fully raised. The brass is still at least .005 too long to the shoulder. I use a Dillon Headspace gauge to check and also attempt to chamber in my tight chambered rifle. Some of them won't size down no matter what, and remain fifteen thou too long, so I just chunk them. The ones which are close are so close that its a tease. Oh the frustration!
I finally got with a friend who has a machine shop. After comparing a factory unfired round, a military round, and a fired case which I sized, we decided to chuck up the die in his lathe and trim a couple thou off the bottom on the die. We tried .005 at first and decided to go ahead and take off 10 thou. When I sized a fired case after that, the Dillon gauge showed the brass going just below the upper step of the gauge and flush with the lower step cut. Perfect!
Moral here? Don't be afraid to make a correction. Fired brass has a certain amount of elasticity and some will spring back to former dimension even after your best attempt has been made to size within spec. In this case, going slightly below SAAMI spec with the sizing die caused the brass to size about right.
This worked for me. I can't say what will work for you. But if you have had the same challenge, trim that die!
Anyone else done this or similar? Discuss.
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