Crimped Primer Pocket
A staked primer pocket on military brass that must be reamed or swaged before a fresh primer can be seated for reloading.
A crimped primer pocket has a ring of metal staked or rolled over the edge of the primer-pocket to lock the original primer in place against the shock and vibration of military use. This crimp is common on military-surplus brass, and it leaves the mouth of the pocket too tight to accept a new primer once the old one is decapped.
Before reloading such cases, the handloader must remove that crimp, either by reaming it out with a cutter or by swaging the pocket back to a uniform diameter with a swage tool. Skipping this step makes priming difficult or impossible and can crush or damage the new primer, so crimp removal is a standard one-time prep step on once-fired military brass.