4runnerman, about this:
Quote:
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Use max loads to fire form cases. Reduced loads too often don't expand the case enough to be safely neck sized anyway. They end up too short from head to shoulder and that leads to incipient case head seperation.
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And what I meant.... Too short from head to shoulder means the shoulder's set back a few thousandths and the case doesn't expand enough to stretch its back end all the way to the bolt face. In rifles whose chamber's are at the maximum headspace, such cases may allow enough head clearance (space between the bolt face and case head) that more stretching starts cracking the case about 1/4" forward of the case head.
How much a case shoulder gets set back from firing pin impact can be measured with a gauge such as the RCBS Precision Mic or Hornady LNL gauges with a caliper. Or use a nylon spacer half an inch long with a 3/8ths inch inside diameter on the case shoulder then measure the distance from case head to the far side of the spacer with calipers. Compare the before and after firing with a primed .308 Win case in your rifle's chamber. Nickel plated case shoulders get set back a lot more than plain brass ones. How much depends on firing pin protrusion, spring strength and the pin's tip shape. It happens.
When there's too much head clearance for a given cartridge that headspaces on its shoulder, head separation is common when setting dies up according to their instructions. Use a good tool to measure your case headspace before and after sizing to see what's happening. Fired bottleneck cases should not have their shoulders set back more than .003 inch else there'll be problems.
Reloader2.... While some folks don't think setting shoulders back (i.e. they only neck size) is important, it is if best accuracy and firearm operation is important. Especially with factory rifles whose bolt faces are not squared up with the receiver. When the case shoulder gets far enough away from the case head from a few firings, the case will bind the bolt when it's closed. A lot of folks think this is a good idea to have a slight amount of binding when closing the bolt on bottleneck ammo. With the typical out of square bolt faces making fired case heads also out of square, that tends to put the initial force of the case head off center on the bolt face making the barreled action whip differently and cause the bullet to leave the muzzle at some tiny angle not desired. And the bolt head doesn't close in the exact same place each time, either. A 1 MOA change in bullet impact is not unusual. So, resize bottleneck fired cases enough to keep that shoulder in the same place and have a couple thousandths head clearance from the bolt fact to the cartridge when its chambered. Best accuracy and reliably chambering/extracting cases happens when this is done. Most benchresters finally figured this out a few years ago and started full length sizing their fired cases reducing body diameters and setting back shoulders about .001" or so.