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Exploding AR9 round

Discussion in 'Rifle Country' started by ponchh, Aug 3, 2018.

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  1. ponchh

    ponchh Member

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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
     
  2. Taurus 617 CCW

    Taurus 617 CCW Member

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    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.
     
  3. 1KPerDay

    1KPerDay Member

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    Nasty. Glad you're ok.
     
  4. RecoilRob

    RecoilRob Member

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    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.
     
  5. 243winxb

    243winxb Member

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    Last edited: Aug 3, 2018
  6. Riomouse911

    Riomouse911 Member

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    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...
     
  7. 243winxb

    243winxb Member

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    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.
     
    Last edited: Aug 3, 2018
  8. ponchh

    ponchh Member

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

    KIMG0107.JPG
     
  9. JeffG

    JeffG Member

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    Maybe both, a double and out of battery. Pressure damage to the gun?
     
  10. ponchh

    ponchh Member

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    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.
     
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  11. ponchh

    ponchh Member

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    That is possible. I am very careful about charges, but you never know
     
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  12. ponchh

    ponchh Member

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    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
     
  13. RecoilRob

    RecoilRob Member

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    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.
     
  14. RecoilRob

    RecoilRob Member

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    4.5 CFE....what bullet? And is it just the picture or are these really dirty? Do you tumble clean between loading?
     
    Last edited: Aug 3, 2018
  15. ponchh

    ponchh Member

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    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.
     
  16. ponchh

    ponchh Member

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  17. someguy2800

    someguy2800 Member

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    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
     
  18. Walkalong

    Walkalong Moderator Staff Member

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    That looks like some serious pressure.
     
  19. ponchh

    ponchh Member

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    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.
     
  20. someguy2800

    someguy2800 Member

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    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.
     
  21. RecoilRob

    RecoilRob Member

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    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.
     
  22. Riomouse911

    Riomouse911 Member

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    Rob, is that what they call a "detonation"? I have heard of them with very light loads in large rifle cases...
     
  23. Elkins45

    Elkins45 Member

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    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.
     
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  24. kozak6

    kozak6 Member

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    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.
     
  25. RecoilRob

    RecoilRob Member

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    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.

    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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