I helped a friend build a lower. He ended up buying a bargain basement upper. Against my wishes. He shot it 5-6 times and it locked up. Couldn't get it to eject the casing and blew the bottom of out of the Pmag.
I was able to get it to eject, stripped it down, inspected and cleaned it. Did not find any issues.
I brought it outside, used the back of my car for cover, and shot it once. Same thing.
I disassembled again. This time I found the firing pin hole in the bolt face blown open. 3/16" maybe? 90% sure it wasn't like that the first time.
How would enough gas get to the mag to blow it apart? Gas rings? Also for the brass to stick in the chamber, chamber issue?
I'd bury it, but for this guy, I think money is tight.
The seller of the upper gave him a new bolt/carrier, but I suggested he send it back to manufacturer to have it checked out.

Was the case (brass) damaged in any way? It sounds like a ruptured case/firing out of battery.

If the head space is to tight it will ramp up pressure, pop primers and rupture the case.

That's what it sounds like, the head space is tight and the pressure is to high, the magazine well it where the gas wants to go.

Get the head space checked by a competent gunsmith! Like now! What is it chambered in/for .223 Remington or 5.56X45mm NATO? If .223 Remington and you all were firing 5.56 in a tight chamber that will raise the pressure, and cause all kinds of troubles!

Was the case sooty and black was the bright and shiny?

ARman

How bargain basement are we talking? Sounds like a head space issue but if you are seeing that behavior the first thing I would do is change out the BCG. What kind of return policy/warranty? Even if they replace the BCG, would you trust it based on the manufacturer?

Thank you both. I double checked battery before I shot it, looked like bolt was fully closed. The brass was sooty.

I think the upper was $199. I thought I had him talked into building a good one, but this came along.

Maybe I should buy a go/no go gauge.

I'll tell him not to shoot until checked out.

They usually blow the bottom off the mag when they fire out of battery or have a case rupture.

By upper do you mean a complete upper? If not, $199 for a stripped upper is not a bargain basement one...

No. It was a complete upper. And IMO not a good deal.

I would return the whole mess to the seller and demand my money back.


What kind of ammo?

quote:

Originally posted by TBH:
I helped a friend build a lower. He ended up buying a bargain basement upper. Against my wishes. He shot it 5-6 times and it locked up. Couldn't get it to eject the casing and blew the bottom of out of the Pmag.
I was able to get it to eject, stripped it down, inspected and cleaned it. Did not find any issues.
I brought it outside, used the back of my car for cover, and shot it once. Same thing.
I disassembled again. This time I found the firing pin hole in the bolt face blown open. 3/16" maybe? 90% sure it wasn't like that the first time.
How would enough gas get to the mag to blow it apart? Gas rings? Also for the brass to stick in the chamber, chamber issue?
I'd bury it, but for this guy, I think money is tight.
The seller of the upper gave him a new bolt/carrier, but I suggested he send it back to manufacturer to have it checked out.

Bad ammo or a bad chamber or both.


Has nothing to do with gas rings. It is unsafe to shoot as-is.

Bad ammo or a bad chamber or both.


Has nothing to do with gas rings. It is unsafe to shoot as-is.[/QUOTE]

Thanks, and agreed. I made contact with the guy and told him not to shoot it.

5.56 ammo in a .223 chamber will spike the pressures and lock things up. (and blow primers)

Were the primers blown out or pierced? (sound like they would have to be if the firing pin hole was eroded that much.)

Over pressure or wrong headspace or too much firing pin protrusion.