Dang ol gun blew up!

[lizerdking]

Well, kinda...

My buddy bought a 300 blackout and we were sighting it in tonight, about 40 rounds in the mag blew out the bottom and the bolt is frozen. Damage in the link below.

The Ammo was from Precision Cartridge out of Hobart, they were their reloads. It sounds like an overpressure event, I was in the house when it happened to him and he can't rememer if the previous shot did or did not sound normal.

I don't want to point fingers at the ammo but at this point I have a feeling that was the culprit, gun was brand new and seemed to be functioning fune up until that point.

Thoughts as to what happened? is the gun salvageable with just a new bolt or should he be worried about chamber / barrel/ other damage?



Imgur

No damage to my buddy save for his toe where the mag landed on it (he was wearing sandles) I'll spare everyone from the pics of damaged man feet.

--edited update--

First pic is a case length from an unfired round out of the batch, i checked a few and they were all this length, is that the culprit? I'm seeing max max case length at least a tenth of an inch under that. The way the case expanded it doesn't appear as if it was chambered all the way when set off, don't AR's have a floating firing pin? Was this the perfect storm of events?

The rest of the pics are aftermath of the blow'd up case/bolt carrier, from what I can tell the damage appears to be limited to the extractor and bolt carrier..



--edited with more pics---

--edited to add pocs of fired cases--

 

[SSGSAD]

I am NOT an AR "expert", but soon I will be .....

First question, did he, or you dissassemble and check, and lube it ?????

 

[Lammchop93]

Maybe it's me, but that gun looks extremely dry. But I still don't think that would have anything to do with it locking up and cracking like that.

 

[lizerdking]

Bolt is frozen in, going to take it down to the basement and try to tap it out in a bit, curious to if their is barrel blockage and howany if there is... My money is on a squib followed by a non squib at this point...

 

[churchmouse]

Bolt is frozen in, going to take it down to the basement and try to tap it out in a bit, curious to if their is barrel blockage and howany if there is... My money is on a squib followed by a non squib at this point...

If you were sighting it in how would you miss a squib round???????

 

[lizerdking]

it was pretty much on at that point, he was shooting 5 shot groups at a distance... couldn't see the holes from the bench, had to walk up to check them after

 

[churchmouse]

it was pretty much on at that point, he was shooting 5 shot groups at a distance... couldn't see the holes from the bench, had to walk up to check them after

Makes sense.

 

[chezuki]

What does the barrel look like. Rifle squibs aren't pretty.

 

[chezuki]

Also, how long is the barrel? The squib would have had to clear the gas port to cycle the next round or it short stroked and he manually chambered another round when there was a problem. Either way, something would have felt and sounded drastically different.

 

[IndyGunworks]

who built the gun?

 

[Tanfodude]

Need pictures of the foot.

 

[churchmouse]

who built the gun?

My thoughts. Was it spec. for those pressures.

 

[lizerdking]

It was a gun show upper, came from the Valparaiso gun show in Feb, can't tell you the dealer my buddy went home for the night to put some ice on his toe and beer in his belly. Barrel was clean of any obstructions and the case tapped out pretty easy after tapping out the bolt carrier. Main post updated with pics and such..

 

[M67]

The gun being dirty wouldn't have anything to do with that. I don't clean my ARs unless they won't run, have one with over 2k and one with over 1k rounds, and more and more suppressed. Crud isn't the issue.

The back of the case looks....bulged. Like it was a piece of full auto brass and it wasn't able to be squeezed all the way down in the resizing die. I had a batch of 308 brass like that, damn things ended up looking like a belted mag. It could just be where it failed, and it did it anyway, but maybe the brass was stressed too much and it gave?

 

[CountryBoy19]

Looks like a OOBD (Out Of Battery Discharge) but that generally doesn't happen on an AR with a locking bolt because the hammer can't get to the firing pin until the lugs are at least partially rotated and locked in. The "symptoms" of OOBD can, in many instances, be caused by over-pressure so that's the way I would lean at this time. Over-pressure could be caused by a number of things.

 

[david890]

If you were sighting it in how would you miss a squib round???????

My 300 Blackout is extremely quiet when using my AAC Cyclone can and subsonic rounds. Enough so that other shooters have commented on its quietness.

If he were shooting in a crowd, then I could understand missing the report. Firing alone, not so much.

 

[david890]

It was a gun show upper, came from the Valparaiso gun show in Feb, can't tell you the dealer my buddy went home for the night to put some ice on his toe and beer in his belly. Barrel was clean of any obstructions and the case tapped out pretty easy after tapping out the bolt carrier. Main post updated with pics and such..

A clear barrel suggests an OOBD to me.

 

[Light]

Looks like the round discharged OOB to me, the rear end of the case looks like it was bulged out from expanding OOB, and then the rear of the case looks like it blew out.
The clear barrel also means it wasn't a squib.

 

[churchmouse]

Firing pin stuck in firing position?????

 

[Sniper 79]

By the looks of it I think she fired out of battery. Is all the brass the same head stamp? Is it new brass or converted?

Just for kicks I got my gun out and it does go click while I held the bolt back a bit and pulled the trigger. I am curious to know what exactly happened here. Next time I load some rounds I will make up a brass case with primer only and see if it will pop off a primer out of battery.

This is scary!