Slam Fires...

blksno

blksno

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Minuteman
    • Mar 15, 2009
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    SD
    #1
    I've never had one, I've never really been all that concerned about one...HOWEVER, I have been testing some new mags to make sure they cycle. I mod some PMAGS for use with my WSSM AR and always test them in my set up before I send them down the line.
    Usually when I do this, I remove the firing pin just to be safe, but this time I didn't and noticed some fairly startling primers.

    I am using Fed Gold Medal Match 210's and Varget, from what I understand...a fairly touchy combo. I'm more than a little concerned with the small dimples in all of my primers. I don't want to have a slam fire any time in the future.

    I did some trial/error checking when I took my bcg out. With the bolt back inside the carrier, (like when the action would be closed on a live round) the firing pin is so "clean" and free moving that I can shake it back and forth and the pin will come out far enough to impact a primer and so when the bcg closes on a live round, the fireing pin moves so freely that it contacts every primer prior to being hit by the hammer.

    Any thoughts on how to fix this or if I should be concerned? It seems that a very small light weight spring around the firing pin, could prevent this but I'm sure with the current design, it would prevent contact completely.

    all of these are still live rounds
    SlamFire.jpg


     
    #3
    Re: Slam Fires...

    Technical notes on the AR10

    From the link...

    FIRING PIN: Similar to the KMC firing pin, but with several key improvements. The firing pin tip bears a short cylindrical surface just behind the tip. This allows the bolt to have a cylindrical section just behind the bolt face, reducing the possibility of sheared primer material jamming into the opening. The KMC firing Pin and Bolt have tapered surfaces at this point.

    The ArmaLite firing pin has a single flange, and a cylindrical section before it that mounts a firing pin spring. <span style="font-weight: bold">The firing pin spring greatly reduces the light firing pin strike produced in M-16 type rifles when the bolt locks, and thus reduces the possibility of slam fire. </span> In addition, it positively prevents incorrect assembly of the bolt carrier assembly. The KMC firing pin has two flanges which makes it possible to install the firing pin retainer in front of the second flange: the carrier assembly appears correctly assembled but the firing pin cannot strike the primer.
     
    #4
    Re: Slam Fires...

    The AR platform uses a free floating firing pin, the dimples happen. The thing is the rounds aren't designed to be chambered over and over again (at least in an AR) and not fired. I've gotten the dimples in once chambered rounds before (.223) and didn't have a slam fire the second time I chambered them, but I fired them the second time. I wouldn't want to press my luck with multiple chamberings.
     
    #5
    Re: Slam Fires...

    flat out scared the shit out of me when i started looking them over.

    Sounds like that ArmaLite set up should be implemented EVERYWHERE. Just makes me nervous now.
     
    #6
    Re: Slam Fires...

    Those dimples are perfectly normal on both AR-10 type rifles and AR-15 type rifles. Those dimples are how we know at work if someone chambered a round. Like Oodin said, don't keep re-chambering the same round multiple times.
     
    #7
    Re: Slam Fires...

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Badshot308</div><div class="ubbcode-body">Those dimples are perfectly normal on both AR-10 type rifles and AR-15 type rifles. Those dimples are how we know at work if someone chambered a round. Like Oodin said, don't keep re-chambering the same round multiple times. </div></div>
    +1. Some primer cups are harder than others. If my memory serves me, Remington has very hard cups, CCI's are pretty hard, and Federals are quite soft and not considered suitable for AR-style rifles. CCI makes a military primer that is extra-hard. So, if you reload and want to minimize this issue, then go with CCI or Remington.
     
    #9
    Re: Slam Fires...

    Found the post from DocGKR I was looking for:

    <div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">A large SWAT team in this area had a failure to fire from an M4 with Hornady TAP ammo during an entry--fortunately no officers were hurt and the suspect immediately threw down his weapon when the carbine went click instead of bang. After the incident was concluded, the team went to the range and expended the rest of their carbine ammo and had one additional failure to fire. This same team had 3 Hornady TAP rounds fail to fire in training a couple of years ago. When Pat Rogers was teaching a class at a nearby agency, there were 5 failures to fire using Hornady TAP ammo. In all 10 cases, there appeared to be good primer strikes, but no rounds fired. On analysis, the ammunition had powder and checked out otherwise.

    However, despite what appeared to be good primer strikes, two problems were discovered. First, when accurately measured, some of the primer strikes had insufficient firing pin indentations. The failed round from the potential OIS incident had a primer strike of only .013"—the minimum firing pin indent for ignition is .017". In addition, the primers on the other rounds were discovered to have been damaged from repeated chambering. When the same cartridge is repeatedly chambered in the AR15, the floating firing pin lightly taps the primer; with repeated taps, the primer compound gets crushed, resulting in inadequate ignition characteristics--despite what appears to be a normal firing pin impression. Once a round has been chambered, DO NOT RE-CHAMBER IT for duty use. Do NOT re-chamber it again, except for training. This is CRITICAL!!!</div></div>
     
    #12
    Re: Slam Fires...

    Those dimples are about twice as big and deep as I'm comfortable with, and I was "raised" on M1 Garands.

    I even had one receiver replaced because it was bad in two ways, one of them relevant here. The bolt raceway was about .05 or so too "low" compared to the receiver legs, AND the firing pin get *too far PAST the bolt face* just before rotating locked. An early hammer strike (if the camming surfaces didn't stop contact) could result in a "dimple" about 25% deeper than what the pics show.

    The AR system has similar functions with the interface of the bolt and bolt carrier. *IF* the firing pin protrusion is deep enough to allow it, I would shave about .005 off the tip. If *not* deep enough, I would look at the pin retraction surfaces and see whether a new pin would reduce the unlocked-position invasion of primer space, or if the BC is off a bit.

    It might be okay now, but I don't see any safety margin for further wearing in of the parts.
     
    #13
    Re: Slam Fires...

    I've seen about ten slam fires with AR type rifles.
    I've personally never had one, but I've witnessed a bunch.

    If you take out your firing pin, the cam pin won't reliably lock or unlock the bolt.
    The lugs may not be lined up properly going into battery (not good), and it may be hard to remove.
    Refrain from removing the firing pin because the BCG needs it to function.

    Slam fires are usually caused by improperly seated "high" primers being ignited on bolt closure.

    Aspire to learn and be competent when making ammunition.
    You don't yet know what you haven't learned yet.
    Many pretend they know it all.

    When chambering a live round in ANY firearm, expect it to go off, sometimes it does.
    This means that it should be pointed in a direction that was already thought out beforehand.

    I'm serious about how many slam fires I've seen.
    No joke.
     
    #14
    Re: Slam Fires...

    Our department has gone back and forth on this.

    Several AR platform "guru's" say it's not a problem and have demonstrated over a hundred chamberings with duty ammo and it still properly functions. Some department's have had failures to fire because the top round was repeatedly chambered.

    I take the middle ground. If I chamber a round more than a couple times it gets rotated in the mag. When I end up with a mag full of dimpled primers the ammo gets traded out. We have had some summers where it only took me a month to go through a magazine.
    wink.gif


    Better safe than sorry.

    ALWAYS, ALWAYS, ALWAYS keep your muzzle in a safe direction when chambering a round.
     
    #18
    Re: Slam Fires...

    I'll tell you this much-
    a number of years ago the Army put out a safety bulletin about slam fires advising regular rotation of frequently chambered rounds to prevent slam fire. I've never personally seen one, but I have to believe if they felt the need to put out a service wide bulletin on it, there must be at least a LITTLE merit to it. We always either rotate "top rounds" to the bottom, toss em or dump them into a range use only box.
     
    #20
    Re: Slam Fires...

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hamilton</div><div class="ubbcode-body">I really have personally seen about ten slam fires with AR type rifles.
    This is a real phenomenon.
    Usually reloader's fault.
    </div></div>

    I'm referencing true slam fire- as in weapon induced, not ammunition induced. Specifically in terms of military ammunition (which I can not recall every seeing primer seating issues)

    I can see how failure to fully seat the primer could be a major cause.
     
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