[Bart B.]

Unclenick's remarks are excellent.

I'll add that if you're using a full length sizing die and setting fired case shoulders back more than .003" from their fired position, any semiauto rifle will soon develop incipient head separation and soon thereafter the head will crack open if not off.

Traditional sizing die instructions say to set the die so the shell holder presses hard against its bottom when full length sizing cases. That sets the case shoulder back too far most of the time. Get an RCBS Precision Mic or Hornady LNL headspace gauge then use it as per instructions. Then fired case length will be a couple thousandths shorter than before it was fired then lengthen one more thousandth growing about .001" or .002" per shoot-size-shoot cycle.

RCBS, Redding and Forster all claim that unsized portion of the case neck that's about 1/32" long helps center the case neck in the barrel chamber. And their bushings float around a couple thousandths sideways; they're not held in line with the die body axis. As that part of the neck is smaller than the chamber neck, it does nothing to center it in the neck. When fired, rimless bottleneck cases are pressed hard into the chamber shoulder where the case shoulder perfectly centers. How well the case neck centers as it floats clear of the chamber neck wall depends solely on how well centered it is on the case neck.

Full length sizing dies with their necks honed out a bit to about.002" smaller than a loaded round's neck diameter center them best. No other sizing die holds the case body in line with its neck sizing part making everything as straight as possible. And cases are decapped and cleaned before sizing so no expander ball's used that typically bends case necks coming up and out of one sized down too far. Forster charges $12 to hone out one of their standard full length sizing die necks.