Tally XD

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.

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rocky

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?

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Nemo Me Impune Lacesset

Link to my kydex builds:http://rocknloadkydex.blogspot.com/

dukalmighty

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

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Tally XD

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.

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BAC

Tally, pm inbound.


-B

Tally XD

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?

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Tally XD

PM recieved!

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BAC

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


-B

rocky

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?

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"In matters of style, swim with the current; in matters of principle, stand like a rock." Thomas Jefferson


Nemo Me Impune Lacesset

Link to my kydex builds:http://rocknloadkydex.blogspot.com/

Tally XD

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.

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