While MkVIIIz is a popular topic...

[Brian Dick]

The hardening in the locking lug recesses is probably worn out. That has nothing to do with stretching. The bolt will set back causing excessive headspace. I think it's mythology that the Mk.VIIIz cartridge has more pressure. The only difference is the 175 grain boat tail projectile as opposed to the 174 grain flat base projectile in the Mk.VII/VIIz.