One wonders if it may have been a reload.

M1icon has a "floating" firing pin. Military primers are designed to accommodate "bumps" from the firing pin without "slam firing". We take a chance when using normal commercial primers in garand reloads.

I shoot reloads for hunting but make sure they are fully seated in the primer pocket. However they will receive a slight dent as the bolt goes into battery. Military spec primers are available for reloading and are the safest route to go.
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