SmallCaliberCentral

While out on a prairie dog shoot last week, my new AR started popping some primers randomly. I was shooting factory Hornady ammo and had several primers pop out of the cases after shots. The rifle is essentially new and only had 20 rounds down the tube of a new Krieger barrel chambered in .204. I never noticed a problem during the first 20 shots and should also point out that the gas block came loose while out in the field. A friend tapped the gas block back into place, since it slid forward after coming loose. Aside from the primers, the gun cycled properly and didn't have any other issues. Is it possible that the gas block isn't aligned properly and that too much pressure is building up in the chamber? Anything else that I should check that would be obvious?

Thanks.

I don't want to sound alarmist, but...this needs attention ASAP.

It sounds like you have two separate issues. The gas block, and for that matter, the entire gas impingement system has no bearing on chamber pressure. Some match shooters completely disable the return gas, and just cycle their guns manually. I can guarantee they're not experiencing primers popping out of spent cases. That said, a loose gas block is indicative that the guy who assembled the gun wasn't paying too much attention. If it's not really inconvenient, this alone would persuade me to return the gun to wherever I bought it, and ask them to check it and fix it.

Primers coming out of factory ammo...that's really weird. I'm going to give Hornady credit for having produced ammunition that's within pressure spec, so I'll rule that out. Barring a really strangely damaged bolt face, I can't imagine how this could be attributed to a defective gun. Were you rapid firing? I'm kind of reaching here, but perhaps you got the gun so hot that the primers came loose in the cases. Of course, by this time, the gun could have started a "cook-off," so I don't know how likely this is.

Is the chamber .223 or 5.56?

I wonder if the gun isn't going fully into battery, and the case head is somehow not fully supported by the breechface, allowing the primer to blow out. Again, I'm kind of reaching here.

If you have any of the ammo left, consider calling Hornady's customer service and tell them what the problem was. They'll probably want you to return any unfired ammo (and maybe some empty cases) for examination. Please let us (at least, me) know about the resolution to this.

Only thing I would add is look at the necks of the spent casings, are they cracked? How fat are they? Do they look cocentric?

Along with the firing out of battery, I may suspect the chamber is short? Just a wild guess there but as mentioned, you have some serious concerns there.

Don't rule out anything unless it is actually checked.