Neck Sizing For MAXIMUM Case Life

Guns Magazine, April, 2001 by Charles E. Petty

Headspace in a bottleneck rifle cartridge is defined as the distance from a datum point on the shoulder to the bolt face of the firearm. Too much headspace in a rifle can be a bad thing, but if you get it just right you can wring the best accuracy possible from the gun and also extend the life of your brass.

Every time a case is fired and reloaded, the brass is subjected to high pressure as it expands to fit the chamber and then is shrunk back down by the sizing die to dimensions that ensure it will fit into the minimum chamber in the ammo specification. Normally, this means that the brass is worked more than it needs to be.

The critical dimension in headspace is established by the shoulder, so full-length sizing almost always pushes the shoulder back, too. But if the case is going to be fired in the same gun, it doesn't need to be completely resized to work well. Neck- or partial-sizing can prolong case life and improve accuracy.

Without some means to measure the headspace in your gun -- and then to use that information to properly adjust the sizing die -- we really are working in a trial-and-error mode. The old-fashioned method -- that still works -- was to start with a case that was fired in the specific rifle and resize it incrementally until the bolt would just close without binding.

A fired case will rarely go back in the chamber, so we begin with the sizing die adjusted to be two or three turns above the shell holder. Size a case and try it in the rifle -- probably won't go -- so the die is turned in by half a turn and the process is repeated until the case will go in fully but the bolt won't close.

You can actually feel how the process is going, so lower the die one-quarter turn and try again until the bolt closes without resistance. It will take quite a few tries to get it right, but you still won't know what the actual headspace is -- just that the brass is adequately sized.

At that point, you could use a neck-sizing die for several loadings, but you would have to go back now and then to make sure the shoulder is still in the right place.