AR slamfire and or OOB incident

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  • GunBum

    Active Member
    Feb 21, 2018
    751
    SW Missouri
    One possibility that’s been overlooked so far…

    If the port pressure is too high, the bolt can unlock before the pressure in the chamber/barrel fall far enough, and the case will bulge as it extracts. This may have nothing to do with firing pin bounce and/or bad primer seating. The first round may have been the one with the high port pressure and the extra recoil cause the shooter to bounce the trigger and do a quick double tap.
     

    Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,282
    HoCo
    One possibility that’s been overlooked so far…

    If the port pressure is too high, the bolt can unlock before the pressure in the chamber/barrel fall far enough, and the case will bulge as it extracts. This may have nothing to do with firing pin bounce and/or bad primer seating. The first round may have been the one with the high port pressure and the extra recoil cause the shooter to bounce the trigger and do a quick double tap.

    The 2nd round was the one I cleared and dropped at my feet. I later picked it up and saw the bulge. All the other spent cases were behind me at 4 o'clock.
     

    GunBum

    Active Member
    Feb 21, 2018
    751
    SW Missouri
    Ok. So it wasn’t the first one with the high port pressure. That doesn’t mean it wasn’t high port pressure.
     
    Last edited:

    Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,282
    HoCo
    Ok. So it wasn’t the first one with the high port pressure. That doesn’t mean it wasn’t high port pressure.

    That could be, High port pressure could have contributed to early bolt release.

    BTW, I ran my load (25.2 gr H335) in a reloading tool and measured how much powder I could get into the round before getting a compressed load and its still below 5.56 pressures which the barrel is rated for but as mentioned, could make it overgassed. All bets would be off on my calculation if the bullet pushed into the case. I do use a crimp on my reloading. I don't know how an AR reacts to over gassing and if that is a thing with an early opening.

    No GO gauge : Pass/did not open (I don't have a go or field gauge)
    Fire Pin Protrusion : .031" average of 5 measurements

    Not sure how to measure the spring.I could put some measurement marks on a dowel rod then push it down on a scale to measure the weight of the pressure after say at different depth measurements of pushing the dowel rod on the spring. This is how I once compared springs when I lost track of a light spring that came with a Dissipator upper that needed a light spring.

    I did a slow release test of 20 times w/ the Trigger to test the trigger reset. That was fine. I had done that at the field right after the incident but it was not a "slow trigger release" as Clandestine suggested.
     

    John from MD

    American Patriot
    MDS Supporter
    May 12, 2005
    22,734
    Socialist State of Maryland
    That could be, High port pressure could have contributed to early bolt release.

    BTW, I ran my load (25.2 gr H335) in a reloading tool and measured how much powder I could get into the round before getting a compressed load and its still below 5.56 pressures which the barrel is rated for but as mentioned, could make it overgassed. All bets would be off on my calculation if the bullet pushed into the case. I do use a crimp on my reloading. I don't know how an AR reacts to over gassing and if that is a thing with an early opening.

    No GO gauge : Pass/did not open (I don't have a go or field gauge)
    Fire Pin Protrusion : .031" average of 5 measurements

    Not sure how to measure the spring.I could put some measurement marks on a dowel rod then push it down on a scale to measure the weight of the pressure after say at different depth measurements of pushing the dowel rod on the spring. This is how I once compared springs when I lost track of a light spring that came with a Dissipator upper that needed a light spring.

    I did a slow release test of 20 times w/ the Trigger to test the trigger reset. That was fine. I had done that at the field right after the incident but it was not a "slow trigger release" as Clandestine suggested.

    This confuses me. When you check the headspace, the bolt should not lock with a NO Go gage.
     

    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,031
    Elkton, MD
    Depending on the gauge manufacturer it's ok to close on a no go.

    Closing on the no go just leads to reduced brass life.

    Some gauge companies the no go is the unsafe maximum.

    With other gauge companies the field is the unsafe max.

    Brand new 700P will and always have closed on a No Go.
     

    alucard0822

    For great Justice
    Oct 29, 2007
    17,643
    PA
    That could be, High port pressure could have contributed to early bolt release.

    BTW, I ran my load (25.2 gr H335) in a reloading tool and measured how much powder I could get into the round before getting a compressed load and its still below 5.56 pressures which the barrel is rated for but as mentioned, could make it overgassed. All bets would be off on my calculation if the bullet pushed into the case. I do use a crimp on my reloading. I don't know how an AR reacts to over gassing and if that is a thing with an early opening.

    No GO gauge : Pass/did not open (I don't have a go or field gauge)
    Fire Pin Protrusion : .031" average of 5 measurements

    Not sure how to measure the spring.I could put some measurement marks on a dowel rod then push it down on a scale to measure the weight of the pressure after say at different depth measurements of pushing the dowel rod on the spring. This is how I once compared springs when I lost track of a light spring that came with a Dissipator upper that needed a light spring.

    I did a slow release test of 20 times w/ the Trigger to test the trigger reset. That was fine. I had done that at the field right after the incident but it was not a "slow trigger release" as Clandestine suggested.

    Re-reading the thread, and pics since my last post thinking it was ammo related, it's all but a certainty to be caused by seating primers like that, and you are REALLY lucky.

    The priming pellet is a little lose under the anvil when they are manufactured, being a pressure sensitive explosive, it makes them safer to handle. Seating the primer snugs up the anvil, and kinda primes the primer, making it sensitive to a pin strike within it's spec. This assumes the primer pocket is also in spec. If the pocket is worn/loose, then they can misfire or hang fire. In this case, the crimp was not swaged out, so they were overly compressed, and end up too sensitive, and seated high, so the bolt face will hit the primer. The bolt face itself can set it off, or the floating pin hitting can light the overly sensitive primer. In this case most likely the bolt face or pin hit and set it off after cycling the first round, the lugs were partially engaged, and it essentially became a really really high pressure "radial delay blowback" with the friction between the case and chamber and a tiny bit of lug engagement being the only thing keeping the rifle from blowing up, it delayed enough that the lugs held peak pressure before giving way while pressure was still high. Usually if it's OOB before the lugs engage, the case ruptures, and kaboom. If the lugs are partially engaged and it detonates, they might slip and get chewed(as pictured), or might hold and look OK. If it kabooms after the bolt is fully in battery, usually don't know other than getting a double, and it cycles "normally". At minimum will need a bolt(maybe a BCG) and barrel, should check everything else carefully, and consider yourself lucky you just need to replace a couple parts and not your face.

    TLDR, SWAGE YOUR CRIMPED PRIMER POCKETS, seating primers incorrectly can be as dangerous as over/under charging, but can be harder to catch. And Melnic owes his guardian angel a beer.
     

    brianns

    Ultimate Member
    MDS Supporter
    Dec 29, 2015
    3,559
    Montgomery County
    I reread through the thread to see any mention of the weight of the bullet. I saw 69grain projectiles reported at least in some. 69grain with H335 max is 24.5grains according to Lyman manual in Remington case. So then you also need to wonder what the load needs to be in a military case (can be thicker walls and less volume). You can get to high pressures/compressed loads pretty quickly.
     

    Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,282
    HoCo
    This confuses me. When you check the headspace, the bolt should not lock with a NO Go gage.

    I did it right, I thought it right but wrote it wrong.
    It did not close on the No Go gauge.

    I reread through the thread to see any mention of the weight of the bullet. I saw 69grain projectiles reported at least in some. 69grain with H335 max is 24.5grains according to Lyman manual in Remington case. So then you also need to wonder what the load needs to be in a military case (can be thicker walls and less volume). You can get to high pressures/compressed loads pretty quickly.

    This load was a 55gr Nosler varminter w/ 25.2gr H335 seated to 2.250" OAL

    69SMK is my more accurate load which I had about 100 loaded that were inspected. Had not been shooting that cause 8208XBR was scarce and I don't like using up when I can't replace. (got a lb of XBR a month or so ago so I can continue). I just don't shoot much in the summer.

    Thx again all.

    Just to reiterate what has been mentioned in all the previous posts, Taking care of my Primers through better inspection and 100% swaging the pockets first should resolve future slam fires. Replacing Bolt and Cam pin on this particular AR should make the gun safer in the future.

    I owe my guardian angel more than a beer. I"ve been much closer to worse things than this before and made it out ok. Did a LOT of stupid unsafe things as a teenager and college student.

    I need to start on my memoirs cause when I pass, my grandkids need to read how Granpa did some crazy Sh17
     

    Doco Overboard

    Ultimate Member
    Based on the original problem description, drawings and written first hand account,former reloading techniques provided by the OP-
    I think the round in question lit before bolt lugs were completely closed.
    The stovepipe and stoppage was a secondary effect of the interrupted chain of events during a normal loading / battery cycle.
    I bet if one could mimic the elongated brass in the chamber it would closely parallel the position of the bolt lugs before they were completely mated with the opposing surfaces.
    Earlier on I provided some additional steps that could be taken as a preventative measure when handloading for semi automatic rifles in regards to primer seating except cleaning primer pockets with a brush.
    Keep in mind as has already been mentioned I think, the legs of the primer have additional clearance for shipping and additional reduction of sensitivity for initial seating.
     

    brianns

    Ultimate Member
    MDS Supporter
    Dec 29, 2015
    3,559
    Montgomery County
    I did it right, I thought it right but wrote it wrong.
    It did not close on the No Go gauge.



    This load was a 55gr Nosler varminter w/ 25.2gr H335 seated to 2.250" OAL

    69SMK is my more accurate load which I had about 100 loaded that were inspected. Had not been shooting that cause 8208XBR was scarce and I don't like using up when I can't replace. (got a lb of XBR a month or so ago so I can continue). I just don't shoot much in the summer.

    Thx again all.

    Just to reiterate what has been mentioned in all the previous posts, Taking care of my Primers through better inspection and 100% swaging the pockets first should resolve future slam fires. Replacing Bolt and Cam pin on this particular AR should make the gun safer in the future.

    I owe my guardian angel more than a beer. I"ve been much closer to worse things than this before and made it out ok. Did a LOT of stupid unsafe things as a teenager and college student.

    I need to start on my memoirs cause when I pass, my grandkids need to read how Granpa did some crazy Sh17

    (For continuity sake for the load data) From the manual I quoted for a 55grain projectile the max is 26grains H335.

    I've seen in some situations where 69-70 grain projectiles already seem compressed even at the lower limits to get to 2.26" OAL, granted that is with Varget and IMR4895.

    Still can't say for sure if the pressure is too high in your situation. Were there other cases where you could see if the primers looked normal as opposed to ultra flattened(the over pressure sign)?
     

    Melnic

    Ultimate Member
    MDS Supporter
    Dec 27, 2012
    15,282
    HoCo
    (For continuity sake for the load data) From the manual I quoted for a 55grain projectile the max is 26grains H335.

    I've seen in some situations where 69-70 grain projectiles already seem compressed even at the lower limits to get to 2.26" OAL, granted that is with Varget and IMR4895.

    Still can't say for sure if the pressure is too high in your situation. Were there other cases where you could see if the primers looked normal as opposed to ultra flattened(the over pressure sign)?

    I did collect the spent brass (out of habit cause I reload). I did inspect them as I was looking for the missing bulged case. All the other cases looked good. Don't forget that the reloading manuals will show 223 pressures and not 5.56
     

    brianns

    Ultimate Member
    MDS Supporter
    Dec 29, 2015
    3,559
    Montgomery County
    I did collect the spent brass (out of habit cause I reload). I did inspect them as I was looking for the missing bulged case. All the other cases looked good. Don't forget that the reloading manuals will show 223 pressures and not 5.56

    Agreed. That's what the Lyman manual says that they load to SAAMI .223 specs. in that data. What cases do you use?
     

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