Need AR help - Several "fail to fire"

This is a discussion on Need AR help - Several "fail to fire" within the Defensive Rifles & Shotgun Discussion forums, part of the Related Topics category; As many of you know I just finished my AR build last week. Took it out shooting a few days ago and sporadically got four ...

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Thread: Need AR help - Several "fail to fire"

  1. #1
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    Need AR help - Several "fail to fire"

    As many of you know I just finished my AR build last week. Took it out shooting a few days ago and sporadically got four or five "fail to fire" out of 70 rounds I put through it. My barrel is chambered 5.56 (CMMG).

    I was using Remington UMC .223 from Wal Mart.

    Yesterday, a buddy of mine gave me a box of Winchester 5.56 and today I fired, or attempted too, them through my AR. I have about 6 or 7 rounds that never would fire out of teh 20 rounds he gave me.

    I have checked the hammer spring. Its fine and installed correctly. I have disassembled the bolt group three times checking for problems. Cant find anything wrong.

    Fired brass looks to be dimpled the same as the unfired (failed) rounds.

    It seems to like to fire the very first round that is chambered, then it tends to not fire the next. After I remove the magazine, clear the weapon and then reload and chamber a round, it seems to fire that newly chambered round, then fail again.

    However, I noticed also that after I had chambered all 20 rounds of the Winchester 5.56, I then loaded up 10 rounds of the Remington .223 from Wal Mart and it fired each and every round without a hiccup.

    I am at a loss here not knowing the AR very well. I dont know what else to check.

    Please give me some pointers as to what to check or look for.
    I am consistently on record and will continue to be on record as opposing concealed carry.
    - Barack Obama Chicago Tribune, April 27, 2004

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  3. #2
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    Sounds like the hammer is possibly failing to lock up sometimes and following the carrier forward. The Win. 5.56 may have a bit more power , helping to to cycle correctly. Check here for lots more advice.AR15.COM :: Forums :: Troubleshooting
    BTW, what FCG brand did you use?
    "In matters of style, swim with the current; in matters of principle, stand like a rock." Thomas Jefferson


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    VIP Member Array dukalmighty's Avatar
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    make sure the bolt is going all the way forward if it isn't the hammer will drop but the firing pin will have either no hit or a light hit.make sure the bolt carrier has plenty of lubrication if ir is slowed up on the cycle when it strips a round out of the mag it will not have sufficient force to close the bolt all the way,if cases are out of spec they may also hold the bolt open a little
    "Outside of the killings, Washington has one of the lowest crime rates in the country,"
    --Mayor Marion Barry, Washington , DC .

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    Quote Originally Posted by rocky View Post
    Sounds like the hammer is possibly failing to lock up sometimes and following the carrier forward. The Win. 5.56 may have a bit more power , helping to to cycle correctly.
    BTW, what FCG brand did you use?
    The 5.56mm was the one I had the most trouble out of. I had much better luck with the .223 Remington.

    I can hear the hammer drop but it just doesnt fire the round. The primer will be dented good but it just doesn't go "boom".

    I think the trigger parts kit is either DPMS or RRA standard.
    I am consistently on record and will continue to be on record as opposing concealed carry.
    - Barack Obama Chicago Tribune, April 27, 2004

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    BAC
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    Tally, pm inbound.


    -B

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    Quote Originally Posted by dukalmighty View Post
    make sure the bolt is going all the way forward if it isn't the hammer will drop but the firing pin will have either no hit or a light hit.make sure the bolt carrier has plenty of lubrication if ir is slowed up on the cycle when it strips a round out of the mag it will not have sufficient force to close the bolt all the way,if cases are out of spec they may also hold the bolt open a little
    Forward assist does no good, of course I cant recock the hammer after I have dropped it though. I have to chamber another round. As before, I hear the hammer drop, just the round doesnt go "boom". The primer will be dented on all rounds.

    Something I just noticed though after inspecting both fired and "dud" rounds. I noticed that the dented but unfired primers seem to be set deeper into the cartridge casing than on the rounds that fired. The fired rounds casings have primers that are flush with the rear of the casing. The unfired rounds look to be set in a slight bit, yet they are very well dented by the firing pin.

    Could these have been set too deep from factory or could they have moved when the firing pin struck them?
    I am consistently on record and will continue to be on record as opposing concealed carry.
    - Barack Obama Chicago Tribune, April 27, 2004

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    Quote Originally Posted by BAC View Post
    Tally, pm inbound.


    -B
    PM recieved!
    I am consistently on record and will continue to be on record as opposing concealed carry.
    - Barack Obama Chicago Tribune, April 27, 2004

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    BAC
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    Hah, took me a while to finish typing. Distractions.


    -B

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    Oops, read the ammo wrong , sorry. I doubt the primer depth matters unless they are really a large amount of difference in primer seat depth. Did you check and re check the firing pin channel? Was the carrier / gun cleaned and lubed well prior to shooting? Does the firing pin have any burrs ?
    Does the hammer lock up every time dry fire/ testing the gun?
    "In matters of style, swim with the current; in matters of principle, stand like a rock." Thomas Jefferson


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    Quote Originally Posted by rocky View Post
    Oops, read the ammo wrong , sorry. I doubt the primer depth matters unless they are really a large amount of difference in primer seat depth. Did you check and re check the firing pin channel? Was the carrier / gun cleaned and lubed well prior to shooting? Does the firing pin have any burrs ?
    Does the hammer lock up every time dry fire/ testing the gun?
    Gun was/is brand new with zero rounds prior to first firing the other day. Gun was clean and lubed. Possibly not lubed enough but it was clearly "wet" with some oil.

    Firing pin and channel is clean and was cleaned prior to both firing episodes. No burrs on pin. Hammer always locks up during dry fire.
    I am consistently on record and will continue to be on record as opposing concealed carry.
    - Barack Obama Chicago Tribune, April 27, 2004

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    are you sure the hammer spring legs are sitting on top of the disconnector pin and not underneath,if the spring doesn't apply enough pressure on the hammer you will get reduced hits on the primer
    "Outside of the killings, Washington has one of the lowest crime rates in the country,"
    --Mayor Marion Barry, Washington , DC .

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    Something else that I just thought of if you push the pin in the hammer can you freely turn it or is it so tight that it will not let the hammer rotate easily,If it doesn't rotate freely it can cause light primer hits and being a new gun may be tight
    "Outside of the killings, Washington has one of the lowest crime rates in the country,"
    --Mayor Marion Barry, Washington , DC .

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    Did you lube the parts prior to assembly? Is the gas tube lined up correctly with the gas post in the front sight base? Is the gas key tight and properly staked? What buffer are you using?
    "In matters of style, swim with the current; in matters of principle, stand like a rock." Thomas Jefferson


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    BAC
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    Unless I miss my mark, he's using a carbine-length buffer with a mid-length upper. I would normally suggest to buy an H buffer ($20) and extractor upgrades (a few bucks), which would be appropriate for a mid-length system with a carbine buffer/stock assembly, but it sounds like the rounds simply weren't firing.


    -B

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    Quote Originally Posted by dukalmighty View Post
    Something else that I just thought of if you push the pin in the hammer can you freely turn it or is it so tight that it will not let the hammer rotate easily,If it doesn't rotate freely it can cause light primer hits and being a new gun may be tight
    I have anti-rotation pins (KNS Gen II)

    Quote Originally Posted by rocky View Post
    Did you lube the parts prior to assembly? Is the gas tube lined up correctly with the gas post in the front sight base? Is the gas key tight and properly staked? What buffer are you using?
    Everything was lubed, probably a little over lubed. Gas tube is definitely lined up correctly. I checked with low pressure air with barrel chamber pugged. Good air flow. Gas key looks properly staked and is tight. Using whatever buffer came with the BCM M4 6 position buttstock kit.


    Quote Originally Posted by BAC View Post
    Unless I miss my mark, he's using a carbine-length buffer with a mid-length upper. I would normally suggest to buy an H buffer ($20) and extractor upgrades (a few bucks), which would be appropriate for a mid-length system with a carbine buffer/stock assembly, but it sounds like the rounds simply weren't firing.


    -B
    Correct. Carbine length. Supposed to be ok with this buffer right? Already upgraded the extractor with the D-fender o-ring. May upgrade with H buffer soon.
    I am consistently on record and will continue to be on record as opposing concealed carry.
    - Barack Obama Chicago Tribune, April 27, 2004

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