Pierced Primers Factory Ammo???

[Orlando]

Going through some of my brass and found a few pierced primers. Ammo is Factory Hornady 75gr Match .223 fired out of my Armalite
M15A4(T) Stainless Match barrel

I checked the firing pin and under a magnifiying glass I can see a very small chip or imperfection.
Do you think the chip in the pin is the result of the ammo or the pierced primer is the result of the firing pin?
I think the dimple in the middle of the primer strike is from the firing pin defect
Heres a pic of the pin


What you guys think??

 

[Geckgo]

Is your weapon set up for .223 or 5.56. The firing pin spring might be a little hostile so that it gets more punch on military primers??? I don't really know, just fishing.

 

[Orlando]

Rifle will fire both 223 and 5.56

 

[Jeff F]

Get another pin and see what happens, it should swap right out and is not expensive. If its only piercing with the Hornady ammo, it could be the ammo. I have seen that little dimple in the middle of fired primers from a number of other AR's.

 

[Orlando]

Yup, firing pin is on order

 

[68wj]

Your imperfection is likely the result of the piercings eroding the tip. It will only make things worse.

My first thought, based on the nature of the piercings, is that your firing pin protrusion is too long and causing a weak point by stretching the primer cup. A new FP is needed ow anyway, and hopefully the protrusion will be good on the new one. I don't have my specs handy to give you the number to look for.

 

[mshootnit]

I had the exact same problem with Hornady ammo with my Armalite as well.

 

[Slamfire]

Hornady is likely using Winchester small rifle primers.

Around 1999 Winchester changed to the brass finish primer, and as they told me over the phone, they made the primers more sensitive to "combat off center firing pin hits".

These brass finish primers pierce at load levels that never bothered the old nickle plated WSR.

My match AR's ate up a hand full of firing pins and I decided brass WSR's were too expensive for me.

Just use your dished firing pin for as long as you can with this ammunition. If these are WSR's, it won't be long before they dish a new firing pin.

 

[Tadracket]

I know you got a new pin on the way. But I'd file the dish out of that one and put it some place safe, JIC ;-)

 

[Jeff F]

I've seen that dish on a number of different AR firing pins, I don't believe it was caused by the pierced primers.

 

[bigedp51]

Military ammunition has staked or crimped primers to keep them from backing out because of the "longer" military headspace settings, commercial factory loaded ammunition does not and "CAN" back out of the primer pocket.

What you see happening is the primer being hit and then backing out of the primer pocket and the firing pin acting like a cookie cuter and punching the center out of the primer. (a double hit) The dimple in the tip of the firing pin was caused by high temp gas excaping from the primer and it ate a hole in the firing pin.

No.1. Check your headspace. And No.2 you may be able to stone the tip of the firing pin back to the correct curvature if the old firing pin is long enough. (you will have a plus and minus firing pin length)

What you see happens all the time on the British Enfield .303 rifles at the longer headspace settings.

NOTE: you also have a plus-minus cartridge manufacturing "headspace" limits and a short case at the lower manufacturing tolerances can have considerable head clearance or "air space" between the bolt face and the rear of the case.

Below is from the Sierra reloading manual.