Originally Posted by
Patrick Chadwick
Your load may be low to the point of being marginal.
If you are full-sizing the cases, and then firing light loads, and there is a head clearance of X thousandths of an inch, then the following happens:
The striker pushes the cases forwards by the amount X.
The striker continues to advance and ignites the primer.
The powder charge is ignited and expands the case enough to grab the chamber wall, but the pressure is not enough to stretch the case and drive the base back onto the bolt face.
The pressure is however sufficient to drive the primer back.
As a result, the primer is backed out by the amount X.
This sequence does not harm the case, and your head clearance is simply the amount by which the primer has been pushed back. But you may notice soot around of the neck, indicating that the powder charge is marginal. If, however, you were to use a full charge, then the case would have been stretched by the amount X, pushing the base back down around the primer, and you would not have seen a backed-out primer.
You may be wondering why I write head clearance, and not head space. Simply because head clearance is the real difference between the shoulder-base length of the actual case and the chamber, whereas head space is the same measurement, but made with a headspace gauge. Since one normally fires cartridges, not gauges, head clearance is the figure that tells you the actual value, as opposed to the (theoretical) gauge value. Real cases have tolerances, so there is no point in aiming for a head clearance of zero, as this could mean that cases from a different manufacturer (or even a different lot) will not chamber properly.
The answer to all this is simple: use an adequate load to ensure proper case expansion and only neck-size the cases, so that after the first firing the cases will have stretched to fit the chamber, less the amount of spring-back in the brass (one or two 1/000 I imagine). Since subsequent cycles are within the elastic range of the brass, the cases will last for many reloads, eventually failing at the neck - which is being continually worked beyond the elastic range. (And bench-rest reloading artists use chambers and bullets sized to avoid even that)
There is only one drawback to this method - since the cases are now "tuned" to fit the rifle, they may not be perfect for another rifle. So if you have more than one rifle of the same calibre, it is very advisable to keep the sets of cases separate and indentifiable (by marking them or using cases from different manufacturers).
This sequence will not have damaged the case in the slightest.