Pierced primers - monitor your brass

[markm]

This is nothing new to long time M4 shooters. Just a reminder that this does happen from time to time.

I was sorting some brass from last week's shoot and started seeing way too many primers that were black in the firing pin dimple.... like a dozen or more.
I started looking closer and found some so bad you can see light through the pierced primer.

I texted Pappabear that we had a bad firing pin in one of the ARs. Turns out it was my Bravo 14.5 middy. Anyway... here's the brass.



The firing pin barely had a little etching on the tip. Just where you could feel it with your finger nail... and barely visible to the eye.

Here's the bolt face which was starting to get damaged at the firing pin hole.

[TXBK]

Your pics aren't showing up. It's time to switch to Imgur. https://imgur.com

Good reminder, though.

[gunnerblue]

Any idea of the round count with rifle and/or BCG?

[markm]

God damned photo bucket. I'll get a new host tonight.

Couple thousand rounds on the gun I'd guess.

[markm]

fixed..

[Pappabear]

I'll tell you it would take a very careful eye to catch this issue without spotting the brass with holes. When Mark first pulled the pin, he was wearing those black gloves he couldn't tell. We were looking for a bur, but it wasn't so much of a bur as channel or separation on the tip. You had to slowly rub your finger nail over the tip to catch it, yet it was enough to start doing damage to the bolt. Very interesting, very subtle.

PB

[Clint]

Hey Mark,

What does the hole in the bolt face measure?

Too much clearance makes pierced primers more likely.

Too much clearance can be from either an undersized firing pin tip OR an oversized bolt hole.

Firing pin tip should be .059 - .060" after chrome.

Bolt hole should be .0625 - .0645"

Once piercing starts happening, both parts can be damaged and may need to be replaced.


Also, thin cup primers and high pressures can contribute to the problem.

[markm]

Yep. I'll try to measure it today. I have a firing pin protrusion gauge too.

[TXBK]

Thanks for getting the pics up.

I assume that is a BCM BCG? Your hand loads w/Wolf primers?

[markm]

For whatever reason, it's a Colt bcg. Not likely the wolf. That gun gets mostly the 62 grain hpbt load which just has cci primers or something similar.