Blown Primer ?

I have been working on my long range shooting and had something really odd happen yesterday. I'm shooting factory Hornady .308 168 BTHP Match ammo in an AR-10. One of the empties had a small perfectly round hole all the way through the exact center of the primer into the case. The round fired fine. The empty literally looked like it had been placed in a drill press and drilled. No backing out of the primer what so ever. This is the only time I've ever seen anything like this. Heck, I've never even heard of this. All of the other empties had dead center strikes of a "normal" depth and I fired another 10 - 15 rounds afterwards and those all looked normal. I've previously fired about 120 rounds through this rifle. I'm thinking some type of manufacturing defect in that single primer. Anyone have any insight into this?

What you had was a "pierced primer". It comes from a hot load or a load too warm for that firearm. If the other rounds look fine, then it could be just one round causing the problem. I would like to see a picture of the other primers to know for sure.

Here's a couple of pics. The pierced primer is the center one and the other two are from the same box.

Those primers are crimped in? Didn't know Hornady did that.

I don't see the primers crimped but Chad was on the right track (as always )...those shells are too hot for your gun. You need to not shoot those.

Yes, the load is a little warm. Since it's in an AR, I'd recommend not shooting it, and sell it or trade it for some other ammo.

I find it interesting that a factory round would be considered too hot. Isn't that a bit unusual?

AR's are prone to pressure sooner than a bolt gun...I don't understand the logistics just know that most of the time if you have a warm bolt gun load odds are it will be hot in an AR.

What specific Hornady ammo are you running? If it's a Superformance load, then it would not surprise me that it's hot. It depends on the load and powder they are running. The Superformance loads use a slow burning powder to achieve max speeds, which also has more powder in the case. This slower burning powder will increase your gas port pressures, which can result in a warm or hot load in a semi auto. This is why you do not run a slow burning powder for gas guns.

For example, when I first started running my 308 Bulk Match ammo, it was a little hot in some AR's and a few bolt guns. Same thing you saw, a pierced primer. So, that tells me I need to back the load down slightly to make sure it is safe in ALL rifles. From my calculations and testing in multiple 308's, the load was fine. It was an aggressive load on the powder, but a little too much for some rifles. So, I backed it down some. No more pressure issues and it still shoots great.

The 7.62X52 Nato round pressure spec is lower than The 308 Winchester round. If something is a little off with the gas operated guns actions can open a little early or late.

Nope, just their plain Match Ammo.

2700 fps for a 168 is a stiff load. My previous "bulk match" was running 2750 with some pressure. So, now it's running right at 2730. But this is my bolt gun load, not an AR. My regular "bulk" is with a faster burning powder and slower speeds, which will lower pressures some.

The Gold standard Federal Gold Medal Match Sierra SMK runs about 2550 fps out of a 20 inch barrel as I recall.

I've seen regular Hornady custom be too hot for a factory bolt gun. I've also got a custom 22-250 that factory cheap Winchester causes a horribly stiff bolt at slower speeds than reloads. There are several variables that can cause high pressure not just the ammo.

good to know, thanks Chad for sharing your expertise