AR Bolt/Carrier Problem

[Clod Stomper]

Has anyone ever seen this happen before? First time it’s happened to me. Locked that sucker up tight.
 

Fortunately it wasn’t in battery with the barrel. I have no idea how I would have gotten it apart if it had been. It was hard enough as it was. I thought I was going to have to cut the receiver open to figure out why it was locked up. 
 

 

[Chucktshoes]

Gas rings are a wear item. They will weaken and blow out with time and use. That’s a pretty catastrophic failure, but not completely crazy. Inspect the inside of the carrier for damage, replace the rings and go about your business. 

[Clod Stomper]

Yeah. These were brand new. This was a first shot test fire. 

[Clod Stomper]

But, that’s what I’m gonna do. I don’t know what else to do. 

[DWARREN123]

Bad material or bad fit?

Check everything out and replace if it is good to go.

Never seen anything like that but my experience is with the M-16 family.

[PoofNoEyeBrows]

I'll second whats already been said. Faulty ring. On the bright side it failed as designed. The ring gave way and nothing else. Being the softest piece in that area I would be surprised if there was any meaningful damage.

[Prod951]

Could his head spacing be off?

[Clod Stomper]

Good question.  I need to check it. But I’m not sure that would have caused that. I also wonder about over-gassing. It’s a pistol length gas system on a 10.5” 6.5 Grendel barrel. 
 

I'm going to drill and tap the gas block for a gas adjustment screw. 

[PoofNoEyeBrows]

How much carbon do you see in reciever and on the bolt carrier group? Any signs of stress on the gas key? the most important question to me would be who did the build. If you bought it as a complete build I would expect it to be good. Something else also came to mind. From what I've seen grendels add substantially more pressure on the gas system in the shorter barrels then 556.

[Clod Stomper]

There really is no carbon. This was literally the first shot fired from a new barrel and bolt. I assembled it. I haven’t bought a complete upper since the ‘90s. 

There is no obvious damage to the gas key, but I’ll check it more closely. 

I am starting to lean toward severe over-gassing/high pressure as the cause. I didn’t measure the gas port, but it looks a bit big for a pistol length system.  That’s why I’m going to use an adjustable gas block. 

[PoofNoEyeBrows]

Bet that solves your problem. The funny thing about that round vs 556 is on one hand 556 has way higher chamber pressure, on the other the grendel sends more gas down the pipe. There's charts out there if you do some hhunting.ive seen listing for return pressure on your barrel length listing 556 in the 9k range but grendel > 12k.

Anyway let us know how the fix goes.