Exploding AR9 round

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ponchh

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50 years shooting, 9 years reloading, never had a problem until yesterday.
The rife is Angstadt receiver set, Faxon 16 in. barrel, Faxon bolt, FM buffer & spring.
Being new to exploding rounds I need a little reassurance that my take on this is right.
Brass was bought new, on it's third reload, but I know brass can go bad at anytime.
Bullet did exit barrel, mag was blown out of receiver, no visible damage to bolt, receiver, or chamber. Both pieces of the brass fell 2 feet from where I was standing.
I am thinking out of battery, not double charge. Am I right.


KIMG0098.JPG KIMG0100.JPG
 
I had something similar happen on a Colt 9mm rifle with a polymer receiver set using factory ammo. The only thing I could concluse was an out of battery discharge. It made a measnof the upper receiver.
 
How hot are you loading these rounds? Remember blow-back operation always allows a wee bit of bolt travel while the pressure is pretty high so they can be harder on the brass.

During reloading of these rounds did you notice any abnormal resistance resizing them? Any bulges that needed to be ironed out by the sizing die? Some chambers are on the large size and will work brass more than others which can fatigue brass more quickly leading to failures.

Edit: Do you have any pics of fired brass....maybe we can see something of interest.
 
Looks like it popped before it made it into the chamber here, too, by the complete failure of the case leaving just a thick case head somewhat intact. Many of the double-charges (in battery) that I have seen leaves a bit more brass attached together. I will surmise this is because it was fully supported when initially fired and still it's somewhat supported by what's left of the chamber when it blows. (Not always, of course).

I'll hope the bolt is clean and the firing pin wasn't protruding through the bolt face and held stiff by crud when the bolt picked up the cartridge...or the hammer fell just before it locked into battery meaning a funky disconnector as posted above.

Glad everyone is ok...
 
The blow back design is poor engineering imo. Fine for a 22lr, not 9mm.

The bold is extra heavy, as is the buffer spring to slow rearward travel of the bolt on firing. This part is fine.

Till it starts moving forward. If the round doesnt make it into the chamber, the inertia firing pin may have enough energy to fire the round?

The AR 5.56 rotating bolt retaines the firing pin till the bolt is locked.
 
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RecoilRob said:
How hot are you loading these rounds? Remember blow-back operation always allows a wee bit of bolt travel while the pressure is pretty high so they can be harder on the brass.

During reloading of these rounds did you notice any abnormal resistance resizing them? Any bulges that needed to be ironed out by the sizing die? Some chambers are on the large size and will work brass more than others which can fatigue brass more quickly leading to failures.

Edit: Do you have any pics of fired brass....maybe we can see something of interest.
Click to expand...


Rounds are close to subsonic. 4.5 CFE
All of the brass fired before this happened look fine

KIMG0107.JPG
 
ponchh said:
50 years shooting, 9 years reloading, never had a problem until yesterday.
The rife is Angstadt receiver set, Faxon 16 in. barrel, Faxon bolt, FM buffer & spring.
Being new to exploding rounds I need a little reassurance that my take on this is right.
Brass was bought new, on it's third reload, but I know brass can go bad at anytime.
Bullet did exit barrel, mag was blown out of receiver, no visible damage to bolt, receiver, or chamber. Both pieces of the brass fell 2 feet from where I was standing.
I am thinking out of battery, not double charge. Am I right.


View attachment 798772 View attachment 798773
Click to expand...
Maybe both, a double and out of battery. Pressure damage to the gun?
 
243winxb said:
The blow back design is poor engineering imo. Fine for a 22lr, not 9mm.

The bold is extra heavy, as is the buffer spring to slow reward travel of the bolt on firing. This part is fine.

Till it starts moving forward. If the round doesnt make it into the chamber, the inertia firing pin may have enough energy to fire the round?

The AR 5.56 rotating bolt retaines the firing pin till the bolt is locked.
Click to expand...


I wasn't in rapid fire. There was at least 2 seconds between the last good shot and the bad round. It was the last round in the mag, so maybe it didn't pickup just right. But still, I didn't think it could fire out of battery because of the AR design. But I was wrong. The rotating bolt is the difference.
 
Riomouse911 said:
Looks like it popped before it made it into the chamber here, too, by the complete failure of the case leaving just a thick case head somewhat intact. Many of the double-charges (in battery) that I have seen leaves a bit more brass attached together. I will surmise this is because it was fully supported when initially fired and still it's somewhat supported by what's left of the chamber when it blows. (Not always, of course).

I'll hope the bolt is clean and the firing pin wasn't protruding through the bolt face and held stiff by crud when the bolt picked up the cartridge...or the hammer fell just before it locked into battery meaning a funky disconnector as posted above.

Glad everyone is ok...
Click to expand...

When it happened I noticed the sound was different, but it wasn't really extreme. My main clue was the mag blowing out, and when I bent over to pickup the mag I saw the brass. That's when that little shiver ran down my back
 
The blowback AR bolt shouldn't allow the hammer to strike the firing pin unless it's fully home, and seeing that rapid fire wasn't being employed I'd just assume brittle brass that failed. The primer looks normal and I can admit to having loaded and fired 9mm's that were so hot the primer dent reformed back into the firing pin hole.....but in a locked breech gun where it tied up (P-35) after about 10 shots when there were so many little sheared discs of primer (when the barrel dropped to unlock) that it finally couldn't hit the primer anymore. So then wanted to burn them up in a Spectre blowback and about the third round separated much as yours did. Blowback action cannot take as much pressure as safely as locked breech guns.
 
RecoilRob said:
4.5 CFE....what bullet? And is it just the picture or are these really dirty? Do you tumble clean between loading?
Click to expand...

Bullet is 124gr hap
Brass is about as dirty as it comes out of my pistols. Velocity is right at subsonic out of 4 in barrel, haven't chronograph with 16 in yet. And maybe never will at this point.
 
RecoilRob said:
The blowback AR bolt shouldn't allow the hammer to strike the firing pin unless it's fully home, and seeing that rapid fire wasn't being employed I'd just assume brittle brass that failed.

I was thinking the same thing, that it couldn't fire out of battery. If it had been under rapid fire, I might try to blame bolt bounce. The brass was bought new, and on 3rd load, but brass can go bad at anytime.
I wet wash with dawn and ss pins only.
Click to expand...
 
I would have to look at mine but I don’t think there is any disconnector or anything to block firing pin travel out of battery on a 9mm AR
 
someguy2800 said:
I would have to look at mine but I don’t think there is any disconnector or anything to block firing pin travel out of battery on a 9mm AR
Click to expand...

I'm going to do some tests tomorrow.
My plan is to use primed only brass, hook it under the extractor, ease the bolt forward, keeping it out of battery and see what happens.
 
ponchh said:
I'm going to do some tests tomorrow.
My plan is to use primed only brass, hook it under the extractor, ease the bolt forward, keeping it out of battery and see what happens.
Click to expand...

The only think I can think of without going to look at it is that at certain point the hammer will hit the bolt rather than the firing pin but I don’t how far that would be.
 
Most of them will have the bottom of the bolt block the hammer from hitting the firing pin until it moves forward enough to give a clear path to it. If the bolt isn't fully home the hammer strikes the bottom and often will then drive it home but might misfire because that energy wasn't delivered to the firing pin. But....I've not owned an AR in 9mm so am just going off of what many others have used.

And...just looked at Hodgdon reloading data and for 124 jacketed they say starting charge is 4.9grns. Going lighter than starting can sometimes cause weird things to happen...especially with fast burning powders. Charge positioning can alter the burn characteristics and in extreme cases even cause a pressure spike enough to scatter the gun. There also is the possibility of bullet setback where the internal volume changes enough to spike the pressure. Or....it was just a brittle case and one of those things. If you keep shooting those cases this might happen again, and should it....probably be a good idea to ditch the rest.
 
Rob, is that what they call a "detonation"? I have heard of them with very light loads in large rifle cases...
 
My AR9 spit out a couple of these. I responded by switching out the carbine tube and filling a rifle buffer full of lead.

upload_2018-8-3_23-5-50.jpeg

These were not particularly heavy loads. I don’t think the AR works very well as a blowback design.
 
Look at the primer. Looks the same as on the rest of the fired brass.

My guess is firing out of battery. That's still pretty scary.
 
Elkins45 said:
My AR9 spit out a couple of these. I responded by switching out the carbine tube and filling a rifle buffer full of lead.

View attachment 798808

These were not particularly heavy loads. I don’t think the AR works very well as a blowback design.
Click to expand...

Nice! Now...if that case hadn't been as elastic...it could (and likely would) have broken at the head like the OP. Might just be what's going on.

Riomouse911 said:
Rob, is that what they call a "detonation"? I have heard of them with very light loads in large rifle cases...
Click to expand...

Yes....but there are many that dispute the 'detonation' theory saying they weren't able to demonstrate it repeatedly in a lab. Can't say for sure...but I was shooting a light 231 load in 45 Colt that got everyone's attention at the range when instead of 'pop', 'pop', it went BANG!! BIG muzzle flash and report...though the recoil wasn't much different (if at all) than the other shots fired. The case looked OK....nothing on the primer to say that something weird had happened...but it DID. Later on I tried a double-charge which I know is way over...but in the 454 SRH was within pressure limits so I wanted to see how it acted. Nothing like the flash and bang that the weird round had exhibited so I'm pretty confident that it hadn't been a double-charge. My single loading regimen eliminates that possibility plus it's one of those things you REALLY need to be diligent to not do. Weird things can happen...and when going below starting loads you're on your own. The IS a reason they listed the 'starting' load where they did...it's not just where they happened to start. Many times they start really low and see ES being very inconsistent and up the load until it becomes within their acceptable window. There is more to it than just max pressure blowing up things.:)
 
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