Burst primers!

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[No caption] - Credit: Archant

I fired my 6.5 Creedmoor using ammunition with small rifle primers & on extraction the firing pin pulled the primer out - what’s happening?

Q: When I fired my 6.5 Creedmoor using ammunition with small rifle primers, the firing pin pulled the primer out on extraction. Have you ever had that problem?

CHRIS PARKIN replies: The firing pin didn’t actually pull the primer out, the pressure within the case almost certainly blew it out or burst the primer – the cup being the weakest point in the cartridge. Moments like this are why most rifles have a gas escape point adjacent to the bolt lugs to allow this kind of dangerous pressure release to vent away from the shooter, avoiding injury.

Have a close look at any other fired ammunition and inspect other primers and also the case head’s rim to see if the brass has at any time flowed and received any kind of impression from the bolt face, where it has slightly expanded into recesses like the ejector plunger or extractor claw cutout.

High pressure will concentrate on any position where the flat, regular face of the bolt is recessed. Look for black soot around other primers and whether they show craters around their strike points. I would suggest having the rifle checked by an experienced shooter, shop or rifle builder to make sure no other damage has occurred.

I have experienced factory ammunition blowing primers in the past and it’s something that the supplier needs to know about. Most will be keen to hear of your problem as it may reflect a flaw with a production batch.