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9mm brass bulging, like SCARY bulging!

Discussion in 'Ammunition & Reloading' started by nubus, Sep 25, 2011.

  1. nubus

    nubus Guest

    So went to the range today to try out and possibly sell some Slide-Fires. Hadn't tried the new toy out on the 9mm Oly Glock mag AR yet so why not. I'll have to say the rate of fire was impressive, but upon inspection of some of the brass I was a bit concerned, to say the least. (see pic) Needless to say we stopped the experiment. Now this was using 115gr Winchester white box and the factory supplied buffer. What I can't verify is if the bulging was a result of premature extraction or actually firing out of battery. I would think an out of battery ignition would flat explode the case. But I'm curious to see what any of you think of this. I would say about ten percent of the cases did this out of a single 33rd magazine.

    9mmbrass.jpg
     
  2. Mark W.

    Mark W. Silverton, OR Bronze Supporter Bronze Supporter

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    Good Lord what ever you did it's not working. I would assume it is pulling the case out before the pressure has excaped the bore.
     
  3. halmbarte

    halmbarte PDX Active Member

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    My guess would be extracting early. The excess pressure is blowing out the weaker part of the brass above the head of the case.

    H
     
    saxon and (deleted member) like this.
  4. Key-Hay

    Key-Hay North Carolina Active Member

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    I would ask the guys at Slide Fires. Maybe the setup is intolerant to the SF. I'm interested in one for my AR .223. Have you tried that yet?
     
  5. tlfreek

    tlfreek Vancouver WA Active Member

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    that's spot on - all mine look like that too. It's a bit tricky on the resizing die tho - you gotta press really really hard.
     
  6. Key-Hay

    Key-Hay North Carolina Active Member

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  7. nubus

    nubus Guest

    Extensively, and to put it simply, they work well.
    And although this thread was not a ploy, we do have them in stock.
    It's easier on a 5.56/.223 because the recoil snap is heavier.
    It takes a little more finesse on the 9mm.
     
  8. Nwcid

    Nwcid Yakima and N of Spokane Well-Known Member

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    When bumpfiring my OA GL AR I had the same problem. Mine would fail to feed though.
     
  9. nubus

    nubus Guest

    Gonna try it on a Colt style setup also.
     
  10. saxon

    saxon springfield Active Member

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    + 1
    had the same thing happn on a few of them

     
  11. deadshot2

    deadshot2 NW Quadrant WA State Well-Known Member

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    This is a situation were the answer is real obvious. The case is being WAAAYYYY overpressured. When the rate of fire increases the pressure in the barrel from the previous round hasn't fully dissapated yet. The next round is chambered, fired, and meets a pressure "wave" that still remains. All this occurs while the fired case is being extracted. In essence, you are using the firearm in a manner that it was not designed for.

    If you continue this "impress your friends" method, I would suggest that everyone stand back, you wear a ballistic vest, face shield, and heavy gloves. sooner or later this will progress from the brass developing a bad case of "muffin top" to a rather dangerous Ka-Boom.
     
  12. jbett98

    jbett98 NW Oregon Bronze Supporter Bronze Supporter

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    If that is correct, how do full automatics function without this occurring.
     
  13. bruzer

    bruzer Grants Pass, OR Well-Known Member

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    FULLY AUTOMATIC WEAPONS are designed by their manufacture NOT to fire above their CYCLIC RATE OF FIRE. I am no expert so I have to ask what the cyclic rate of fire on the weapon in question is?
    Here is the definition of cyclic rate of fire:
    Cyclic rate

    This is the mechanical rate of fire, or how fast the weapon "cycles" (loads, locks, fires, unlocks, ejects). Measurement of the cyclic rate assumes that the weapon is being operated as fast as possible and does not consider operator tasks (magazine changes, aiming, etc). When the trigger is squeezed, the rate at which rounds are fired is the cyclic rate. Typical assault rifles have a cyclic rate of 500–900 RPM. Typical infantry machine guns have rates varying from 600 RPM to 1,200 RPM. M134 Miniguns mounted on helicopters can achieve rates of fire as high as 50 rounds per second (3,000 RPM).

    If you make a weapon shoot FASTER than its cyclic rate you are going to have problems. Bulging cases might just be one of those problems.
    Mike
     
  14. deadshot2

    deadshot2 NW Quadrant WA State Well-Known Member

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    The cyclic rate for this design of firearm with 5.56mm ammo is just under 1,000 rounds per minute max.

    One solution for this problem might be the use of a different buffer. Something like an Enidine hydraulic buffer could be used to slow the rate of fire to the point that the pressure has diminished sufficient to prevent this bulge.
     
  15. halmbarte

    halmbarte PDX Active Member

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    Sorry, but you're wrong about the cause of the over pressure. Dead right about taking precautions for a OOB case rupture.

    For you to be right the barrel would have to retain pressure after the bullet has left the bore AND after the fired case has been extracted (barrel now has a hole at both ends) fired case ejected, bolt reaches full recoil, strips the next cartridge, feeds the next cartridge, and the bolt goes into battery, AND the firing mechanism has time to fire the next cartridge.

    In your theory, the barrel has to retain pressure while everything listed above is happening. I just don't see it. The timing is all wrong.

    H
     
  16. nubus

    nubus Guest

    Thinking about trying an H3 buffer and different ammo.
    Of course with extreme caution...
     
  17. Gunner3456

    Gunner3456 Salem Well-Known Member

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    I believe that shell extracted before the bullet left the barrel. Why, is another question, but if it's a spring operated blowback, I'd try a stronger spring.

    That doesn't mean I'm right. That's just where my mind goes, first reaction.
     
  18. Key-Hay

    Key-Hay North Carolina Active Member

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  19. deadshot2

    deadshot2 NW Quadrant WA State Well-Known Member

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    You are using the 5.56mm/.223 example when the problem is with a 9mm.

    I know that the standard AR-15/M-16 fires with a locked bolt that has to be rotated before the round can be extracted. Very familiar with this firearm as I am the proud owner of several.

    The 9mm versions are blow back operation and rely on the bolt/spring/buffer to prevent issues like this. In short, the cyclic rate has been exceeded and the case is still "pressured" when it is being extracted.
     
  20. nubus

    nubus Guest

    Although I like this line of thought, why would repeated "fast" fire cause the blowback action to extract sooner than with "slow" repeated fire?
    I also am drawn to think premature extraction is to blame, I think legalizing SBRs in WA would also resolve the issue. ;)
    Shorter barrel = less or no pressure upon extraction, just a thought.