AR slamfire and or OOB incident

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  • Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,282
    HoCo
    Did the bullet clear the barrel?

    If the case did not rupture, there was not a lot of pressure. So either it was an early unlock or if significantly out of battery, then there was not a lot of pressure generated.

    Yes, I both felt "near normal" recoil, plus I opened it up to look for obstruction. I am currently feeling like it was an early unlock that caused the bulge.

    You said there was a double fire. Soft primers will increase the risk of a slam fire, but you still need the firing pin to stick out, either because its dirty or because of hammer follow (hammer follow because something is wrong with the disconnect or FCG), or some issue with the firing pin/BCG itself.

    I inspected the trigger group last night and all looks good as far as springs and such. I also repeated the disconnector test about 50 times and it never let go when returning the trigger forward after it grabbing the hammer back.
    Firing pin did have some carbon build up on the face that hits the bolt on the inside. I cleaned that and it seems to not stick so much. In my early 223 reloading, I had not done so great of a job swaging pockets. I once and a while had deformations of the primers when forcing it in. I may not have been so diligent in tossing rejects like I am now.

    I feel strongly until ruling things out (which may never happen) that 2 things are at play. Sensitive/deformed/faulty primer and something wrong with the gun. It could be just one of the two and a 1 in a 10,000 instance. who knows

    Most everyone who spends time with an AR knows how when you load a round, the primer gets a little tap/divot on it. Nearly all ARs will tap the primer with the firing pin when loading a new round.

    I started late last night pulling loaded cartridges off my stripper clips to visually inspect. I have a number of loads for 223, Cheap armscore plinkers, Xtreme bullet fmj plinkers, Nosler varminter (more accurate) and 69gr SMK.

    I have some boxes I reloaded over 4 years ago that were tucked into the ammo cabinet, In an effort to try to shoot the old stuff first from plinking guns, I had moved those into and onto the top of the ammo cans sorted by loads.

    The "undisclosed" number I will inspect will keep me busy as I do it in small chunks.

    I also have more that I prepped and primed during the beginning of Covid while listening to Zoom meetings for work. I'm going to inspect those too.
     

    brianns

    Ultimate Member
    MDS Supporter
    Dec 29, 2015
    3,559
    Montgomery County
    Check the condition of the cam pin and the slot it rides in. I'm not sure if that can help the bolt to unlock too early upon firing if it's out of spec.
     

    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,031
    Elkton, MD
    Many things could be wrong. I suspect the ammo before the weapon.

    If there's a malfunction or kaboom and reloads are present, it's likely the reloads.

    Reloaders often get angry about this when I say the above about reloads, but they probably haven't seen what I have.

    You may already checked these things:
    You measure the action spring?
    Close on a 5.56 Go Headspace Gauge?
    Firing Pin Protrusion?
    Do a FCG test with a slow trigger release?
    Original M16 FCG and Springs?
    Original Firing Pin? How's the tip look?
    What tool you use to install the barrel?
    FPRP bent?
    Firing Pin move freely?
    Pin Gage the Firing Pin hole in the Bolt?
    Original Extractor and Ejector Springs?

    There's more to ask but I'm exhausted from a 29 hour weekend class, and I'm not very sharp right now. My apologies.
     

    Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,282
    HoCo
    Brians, Clandestine,
    Thx for the suggestions.
    Entire BCG and upper assembly is from the M16 Kit. Barrel is new I installed myself with Wheeler tools (came with FSB installed) Reaction rod used for brake
    FCG is NOT original parts, Spare parts from a standard AR kit I put a Giessele on another AR

    I think I can work on checking most of that stuff but may be limited on what tools I have to check them all.
    I need to look up how to perform some of Clandestine's list. Always willing to learn something new :)
    Will post more pics


    Clandestine, Yes, reloads I totally have not ruled out that being a factor here, And Again think it was part of a combination of factors. I strongly think it was a major contributing factor to the initial slam fire that happened.
     

    alucard0822

    For great Justice
    Oct 29, 2007
    17,643
    PA
    Was about 1/2 way through thinking "must be reloads with federal primers seated too high". If that is the issue, they will light off just by chambering, Doesn't take much, the high primer takes a hit across the face from the bolt, might light off just from that, but soon as the floating firing pin touches it, the primer is tight against the bolt face, and especially softer primers will light. could also be a burr around the firing pin hole, headspace, or FCG issue, I would CAREFULLY check over the BCG and FCP then try factory ammo. If factory ammo runs fine pull the bullets on that entire lot of reloads. Primer seating is probably second only to over/under charging that causes guns to blow up from reloads, it is also tougher to catch when reloading, but if the primer feels at all like it protrudes, then don't shoot it.
     

    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,031
    Elkton, MD
    Brians, Clandestine,
    Thx for the suggestions.
    Entire BCG and upper assembly is from the M16 Kit. Barrel is new I installed myself with Wheeler tools (came with FSB installed) Reaction rod used for brake
    FCG is NOT original parts, Spare parts from a standard AR kit I put a Giessele on another AR

    I think I can work on checking most of that stuff but may be limited on what tools I have to check them all.
    I need to look up how to perform some of Clandestine's list. Always willing to learn something new :)
    Will post more pics


    Clandestine, Yes, reloads I totally have not ruled out that being a factor here, And Again think it was part of a combination of factors. I strongly think it was a major contributing factor to the initial slam fire that happened.

    The RR can lead or amplify barrel extension clocking which can allow for partial OOB firing. Especially when timing a GI barrel nut. I'm not saying you have bad tools or did something wrong, just explaining the tools and techniques can allow for bad things to happen.

    You are taking advice well so you have a leg up on most shooters who have problems like this.
     

    Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,282
    HoCo
    The RR can lead or amplify barrel extension clocking which can allow for partial OOB firing. Especially when timing a GI barrel nut. I'm not saying you have bad tools or did something wrong, just explaining the tools and techniques can allow for bad things to happen.

    You are taking advice well so you have a leg up on most shooters who have problems like this.

    I am certain I used the wheeler receiver clamp when installing the barrel, I thought the Reaction Rod was NOT for installing a barrel and torquing the nut(or was I incorrect?)

    So, when the bolt pushes all the way in, I was trying to compare how the bolt lugs rotate and center up with the barrel. I only spent a few minutes looking at it last night trying to look at the Retro build (the problem AR) with my son's Delton factory built upper and bolt that came with it. How much the Barrel might be canted/timed as well as how much play the Pin allows the bolt to rotate when fully extended are things I may be able to compare, but with my experience may be hard to measure. I'll start by checking it out but also see if I can take pics that may be able to show differences.
     

    Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,282
    HoCo
    Some items investigated tonight
    First up I inspected loaded rounds pulling from stripper clips for an hour. Found a number of primers I did not like and pulled out. None were high but some were force seated to the point they looked like they flattened out or deformed in some way.
    Here are pics of a few
    8d9fd6ea813d7bb97932ad7d67cd6ace.jpg


    I also looked at how much rotation wiggle the bolt would move when fully pushed in (closed position). It was noticeable compared to a nearly new bolt. Swapping parts to isolate the issue it was the cam pin shown below. You can see the wear marks.
    6aab2e86b0c4e635badf8c8c65cb01b9.jpg


    Firing pin. Left is the surplus M16 firing pin. Right is the nearly new Delton
    117decf6d28d8b7f4f8ba3beafbe54b2.jpg


    I don’t have a tool to measure firing pin protrusion or a small pin gauge to measure the hole but here is a pic. (Lube removed so I could take better pics)
    2fceef6c917b4ddfc01cd2cbce7b4d1f.jpg


    Here is a pic of a visual check of the inside of the upper
    16cc484d11e9271f423dd9f0c7e4b0d4.jpg



    Sent from my iPhone using Tapatalk
     

    atblis

    Ultimate Member
    May 23, 2010
    2,011
    Looks like you’re trying to load cases that haven’t had the primer crimp removed.
     

    John from MD

    American Patriot
    MDS Supporter
    May 12, 2005
    22,734
    Socialist State of Maryland
    I second what atblis said about the primers. If you are swagging your primer pockets, you are not swagging them enough or your seating stem is not square. As for the other wear, I have shot M16's both semi and full auto with way more wear on it than you have and had no malfunctions.

    I'd say there is a good chance that the issue was early ignition from a high primer.
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,818
    Some items investigated tonight

    I don’t have a tool to measure firing pin protrusion or a small pin gauge to measure the hole but here is a pic. (Lube removed so I could take better pics)

    Yes you do. Use the tail end of your digital caliper. Measure to the bolt face, then measure to the tip of the firing pin while you manually push it through the pin hole. A little subtraction and you have your protrusion measurement.

    Anything between .028 - .036 is a go.
     

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    Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,282
    HoCo
    Outrider, Duh I should have thought of that but did not. Will check that tonight

    John, I do agree about swaging but I still contend that multiple factors caused the OOB. First off , the slam fire. I put odds on a faulty primer pocket swaging and me forcing the primer in causing the primer deformation and the slam fire. That can explain the slam fire. Remember what I posted, I pulled the trigger once and 2 cartridges ignited, one after the other. The bulge is a secondary effect of the slam fire. I feel strongly that what I would call wear stack up (is there a better description?). Like tolerance stack up. Small deviations adding up allowed the bolt to open up prematurely but not necessarily at the time of initial ignition.
    My current theory is this.

    Faulty primer due to my reloading process I used to use a few years ago caused the slam fire.
    Wear on the back of the bolt locking lugs, the wear on the bolt cam pin, movement of the bolt during ignition and possibly some bolt bounce allowed the early release of the bolt before pressure came down to safe levels

    A couple years ago I was not swaging 100% of the cases, I was trying to test them by hand with the swager tip and then swaging the ones I rejected. Or I was marking the bags of picked up reloads that I had fired once only to find that I once and a while would pick up cases that were not from my gun.I gave up on that and started swaging 100% of them late 2019 and into 2020

    This morning I inspected an entire can of plinking reloads and they all looked pristine.

    Since I have shot thousands of 223 reloads of mine I’m betting if I took any rejects I had and run them in another gun I may be able to get a slam fire but doubt I could get a bulge. I’ll just pull them apart though cause I don’t have the time to set up a safe contraction to run such a test.

    Sent from my iPhone using Tapatalk in
     

    Doctor_M

    Certified Mad Scientist
    MDS Supporter
    Melnic... while I don't have a lot of technical expertise to offer here with regards to you issue, I thank you for posting all of the details (and all of the insightful comments from others)... I am learning a lot just by listening to this conversation. As always, Clandestine' s world-class expertise is incredibly valuable.
     

    Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,282
    HoCo
    Melnic... while I don't have a lot of technical expertise to offer here with regards to you issue, I thank you for posting all of the details (and all of the insightful comments from others)... I am learning a lot just by listening to this conversation. As always, Clandestine' s world-class expertise is incredibly valuable.

    Your welcome, I figured this was a significant enough instance that I did not want to hold things back. Maybe someone else can learn something off of this. One could EASILY be embarrassed by the reloads I found that have now pulled off and rejected, but hey, live and learn. Maybe I'll help someone else from making the mistakes I made in the past. As an Engineer, I'm often drawn to a mystery and working to troubleshoot my way out through it. In my younger days, I would have said "hmm, that's weird" and kept shooting.

    There have been a few 223 reloading posts in the past couple years and people mentioned swaging and how its a pain in the arse. That is what took me to 100% swage last year.

    Current plan I have is to replace the bolt assembly (not the entire BCG) and Cam pin then run it with some factory ammo (all I have is Wolf and some Remington UMC) then if all ok, my inspected reloads. Gonna start off w/o may hand on the forearm and just bench shoot it. I have some time before implementing the plan to continue doing the checks Clandestine and others have layed out in case I need to do something else also.
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,818
    I don't want to leave the wrong impression here, OOBs are a serious issue. But we aren't positively sure this was one. I'm not saying it wasn't. We just don't have enough evidence to cement this. It could have very well been simply a double-tap(way more common in ARs than slam-fires) and an ugly piece of brass(which we unfortunately no longer posses).

    Be that as it may...

    I only have one last suggestion to offer to Melnic and any other reloaders out there who deal with crimped primer pockets. I've gotten into the habit of not only swaging the pockets, but also chamfering the mouth of the pockets. The purpose is to get rid of that pesky 'rim' that remains from the crimp. Often times as we go to seat a fresh primer, the primer sometimes snags on the rim and causes the primer to enter the pocket crookedly. That usually results in deformed, poorly seated primers which can lead to all sorts of mischief. It's an extra step, I know, but it's the safest bet. Trust me. I'm half way through prepping a 5 gallon bucket of once fired 5.56/.223 brass, most of it crimped.

    Hope this helps...
     

    Doco Overboard

    Ultimate Member
    The use of a primer pocket uniforming tool will also help to relieve and square the primer pocket bottom for insertion of the new primer to a suitable depth without over sensitizing a primer unexpectedly.
    The one I use is hand turned but their may be something available that works with other powered case prep tools.
    By using the tool depending on how it measures up,it could also be and early indicator that pocket swaging has been done completely to remove the annular crimp or if more attention is needed.
    Luckily the operation only needs to be performed once.
     

    cornstalk

    Active Member
    Mar 13, 2013
    138
    I haven't read all the replies, but it seems obvious that: 1) From the way the second case "fire formed" being only partway into the chamber, it had to have fired OOB, 2) The FP cannot come into contact with the primer when the bolt is OOB unless it's broken and the front piece is protruding from the bolt face. SO the first thing I would do is pull the cotter pin and inspect the FP.
     

    Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,282
    HoCo
    I haven't read all the replies, but it seems obvious that: 1) From the way the second case "fire formed" being only partway into the chamber, it had to have fired OOB, 2) The FP cannot come into contact with the primer when the bolt is OOB unless it's broken and the front piece is protruding from the bolt face. SO the first thing I would do is pull the cotter pin and inspect the FP.

    No you did not read all the replies :)
     

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