[marcglock30]

Hi all. I have a fully functional AR-9, but just built another. Both started as 80%lowers, and finished using easy jig gen 2. First upper built by me, second one ordered as a pre-assembled complete upper. The new rifle blew holes in the sides of brass casings, and sprayed hot powder and fragments to the shooter to my right at the range. Also chewed up the top of my mag, and the buffer tube blew out in the back, from what appears to be buffer overtravel. Used standard AR buffer tubes, and heavy 9mm buffers and springs with both builds. Any ideas? Thanks.

 

[fixitfred]

Without examining the gun and not having an extensive enough background let me venture some guesses. The cases show out of battery ignition. The bolt may not be locking up properly causing the problems you described.

 

[Square target]

That looks like it was fired out of battery. I would check first to see if your firing pin is moving freely. Never seen a buffer tube blow out, not sure if out of battery firing can or will do that but I'm thinking no.

 

[Stamps6]

Bear Creek should be able to help you. It’s a family run business and have a decent reputation. I have one of their AR’s and it’s great.

 

[AgedWarrior]

Interesting! By the looks of the cases it was about 3/8” out of battery. I am going to look more later, but I am not certain the hammer can actually reach the firing pin with the bolt that far back. Thus it would be more of a stuck firing pin scenario or slam fire (no), but no comment about gun firing premature to actual trigger pull. The other thing I was thinking was the disconnect losing its hold as the bolt moves forward, but, again, that would be a premature firing. And none of this explains the buffer tube blow out. :confused5:

 

[Zhills]

If it was an out of battery ingition, then the bolt was not locked and flew back and pushed the buffer tube spring out the back. A lot of things come to mind that could be wrong but I would be looking at the bolt, cam locks, chamber, head space, etc. Question: How many times was the rifle fired but the buffer tube fail?

 

[AgedWarrior]

If it was an out of battery ingition, then the bolt was not locked and flew back and pushed the buffer tube spring out the back. A lot of things come to mind that could be wrong but I would be looking at the bolt, cam locks, chamber, head space, etc. Question: How many times was the rifle fired but the buffer tube fail?

Okay...but the AR9 is blowback system anyway, so how does an out of battery firing cause more reverse thrust on the bolt than a proper firing? How would it cause the buffer tube to blow out? It would seem, in my thinking, that either the buffer or spring might have been wrong or faulty to allow it to slam into the back of the tube...course, that’s just my thinking.

 

[RMLamp]

This may be a stupid question but have you checked the barrel for obstructions?

Are you shooting factory ammo or reloads?

 

[Zhills]

The lugs on the bolt hold it in place while ignition takes place and the lugs offer some resistance when the gas system pushes the bolt back. If the lugs were not locked, which the pictures indicate and the shell ruptures, which the picture shows, you have the entire charge of the shell slamming the bolt back against the buffer tube. The 9mm in a pistol generates 35,000 psi of chamber pressure. In my opinion, the OP was very lucky the bolt did not rupture the back of the upper receiver.

 

[AgedWarrior]

The lugs on the bolt hold it in place while ignition takes place and the lugs offer some resistance when the gas system pushes the bolt back. If the lugs were not locked, which the pictures indicate and the shell ruptures, which the picture shows, you have the entire charge of the shell slamming the bolt back against the buffer tube. The 9mm in a pistol generates 35,000 psi of chamber pressure. In my opinion, the OP was very lucky the bolt did not rupture the back of the upper receiver.

But, that was my point, there is no gas system on an AR-9, they are simple blowback guns. AR-9’s are not direct impingement they are simple blowback operation utilizing a heavier buffer and springs. If the case ruptured, which they did, the majority of the gas pressure was vented out the side, throwing particles at his neighbor on the right and damaging the mag as the OP described, instead of pushing the bolt back. If, at some point there was a squib stuck in the barrel as per RMLanp’s question, that might explain it all a bit better. I could imagine the bolt slamming back quite hard in that case and possibly fouling the chamber so the next round could not go into battery...but hey, I am just an amateur guessing.

 

[Zhills]

"The 9mm in a pistol generates 35,000 psi of chamber pressure." and this pressure was not in the chamber but in between the bolt and chamber. Only a very small part of that pressure is used to push the bolt back, whether it's blow back or gas tube. There are many pictures on the web of firearms with damage from out of battery ignition and some are severe. I would love to see more pictures of the upper receiver (inside and out), the bolt, and a shell in the chamber (no bolt installed).

 

[AgedWarrior]

I have no doubt the receiver is likely damaged too...maybe the OP would provide some pics other than the brass...you could ask.

 

[RMLamp]

Looking at AR-15 9mm blowback BCG images online I don't see any with lugs on them. It would be nice if the OP posted some more images of his AR setup and damage caused by these case ruptures.

 

[marcglock30]

Hi all. Thank you for all of the feedback. I will try to provide more info and pictures. Ammo was brand new Win USA hard ball type. Upper was brand new, complete from factory. Entire upper has been sent back to Bear Creek since original post. Their reply time was delayed for my liking, so I wanted to reach out to the group while waiting. Upper was fired only four times. Original shot, switched mag, tried with bullet in chamber with mag dropped, and one with remaining in-tact mag and my older lower. Buffer tube blew on last shot. Added one more of the ejected brass pics, too.

 

[marcglock30]

More pics

 

[marcglock30]

One more pic showing apparent gap in new upper compared to flush fit in old upper

 

[AgedWarrior]

Hi all. Thank you for all of the feedback. I will try to provide more info and pictures. Ammo was brand new Win USA hard ball type. Upper was brand new, complete from factory. Entire upper has been sent back to Bear Creek since original post. Their reply time was delayed for my liking, so I wanted to reach out to the group while waiting. Upper was fired only four times. Original shot, switched mag, tried with bullet in chamber with mag dropped, and one with remaining in-tact mag and my older lower. Buffer tube blew on last shot. Added one more of the ejected brass pics, too.

Thanks for the pics. Did you by chance examine the barrel before you sent the upper back? How did it look? Clear?

 

[Zhills]

Thanks for the additional pics. It does appear that the rounds were not seating far enough in the chamber. Glad you were not hurt or anyone around you. I'm sure we would all like to hear what Bear Creek tells you.

 

[RMLamp]

Manufacturer got the headspace wrong, wonder if 380 would seat properly.

 

[marcglock30]

I will definitely keep you all up to date when I hear back from Bear Creek. I did not inspect the barrel. I probably should have, but I was more fixated on the apparent gap and bullet not seating correctly into the chamber.