Page "Handloading" Paragraph 82

Since the case is the single most expensive part of a loaded round, the more times a case can be re-used, the better.

Cases that are loaded to a moderate pressure will generally last longer, as they will not be work hardened or flow under pressure as much as cases loaded to higher pressures.

Use of moderate pressure loads extends the life of the case significantly, not to mention saving quite a bit of wear and tear on the barrel.

Work hardening can cause cracks to occur in the neck as the hardened brass loses its malleability, and is unable to survive swaging back into shape during the resizing operation.

Rifle brass tends to flow towards the neck ( this is why rifle brass must be trimmed periodically ) and this takes brass away from the rear of the case.

Eventually, this will show as a bright ring near the base of the cartridge, just in front of the thick web of brass at the base.

If brass is used after this ring appears, it risks a crack, or worse, a complete head separation, which will leave the forward portion of the brass lodged in the chamber of the gun.

This generally requires a special stuck case removal tool to extract, so it is very undesirable to have a head separation.