Rifle won't cycle properly... HELP!

[Pas Tout La]

I pinned an assembled upper and lower together and dropped in a BCG and installed the buffer kit. Shot 3 rounds the other day with no issue. Today it would not cycle consistently. First shot ejected but didn't load another round. I pulled back the charging handle and fired 3 rounds flawlessly. Then it failed to cycle again. Any suggestions on a possible cause?

 

[jasonj5313]

Mag issue?

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[LSUSMC]

Did you try:

different types of ammunition?
multiple mags?
lubrication?

That type of failure is usually indicative of a magazine malfunction or gas starvation but it could be scores or other issues.

 

[rcm192]

Trigger spring or group assembled correctly? Could be a loose gas key or gas tube, missing gastube roll pin.

 

[Poorboy504]

It may be that the system is undergassed. What setup is it? Some midlength 14.5 inch barrelled system may not function reliably with underpowered ammo such as .223 wolf and tula. What weight buffer are you using? A combination of 14.5 midlength and heavier buffer may cause the system to short stroke. Most manufacturers overgas but some such as BCM have milspec gas ports and as such recommend using 5.56 ammo. You can try a carbine weight buffer to see if it will cycle reliably. But first inspect the gas system for any obvious irregularities such as a missing roll pin.

 

[Slimak707]

Which direction is the brass ejecting? 1? 3? 5 o'clock? It'll tell you under or over gased.

 

[sgt z]

bolt rings could be lined up

 

[Pas Tout La]

It may be that the system is undergassed. What setup is it? Some midlength 14.5 inch barrelled system may not function reliably with underpowered ammo such as .223 wolf and tula. What weight buffer are you using? A combination of 14.5 midlength and heavier buffer may cause the system to short stroke. Most manufacturers overgas but some such as BCM have milspec gas ports and as such recommend using 5.56 ammo. You can try a carbine weight buffer to see if it will cycle reliably. But first inspect the gas system for any obvious irregularities such as a missing roll pin.

It's a PSA mid length 16". It's on a New Frontier lower that was already assembled. I'm actually not 100% on the buffer weight. I'll have to check it out tomorrow. I was shooting Winchester 556.

Which direction is the brass ejecting? 1? 3? 5 o'clock? It'll tell you under or over gased.

It was around 4 o'clock. Landed about 3ft from where I was standing.

 

[Slimak707]

4 o'clock has plenty of gas. Probably mag issue. Have you tried other mags?

 

[jasonj5313]

It's a PSA mid length 16". It's on a New Frontier lower that was already assembled. I'm actually not 100% on the buffer weight. I'll have to check it out tomorrow. I was shooting Winchester 556.



It was around 4 o'clock. Landed about 3ft from where I was standing.

What type of mag are you using?

Slap a loaded mag on the ass, if the top round moves you have a problem.

A factory assembled upper souldnt cause failure to feeds.



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[Pas Tout La]

Thermold mags. I have a couple USGI mags ill try in the morning to just for the Hell of it. I'm completely new to ARs so I'm lost.

 

[Ben Segrest]

Maybe it's not all there.

 

[Poorboy504]

I think you found the culprit. Thermold mags are designed to be semi-disposable for the Canadian military. The plastic feed lips tend to bulge after some use and render the mags annoyingly unreliable. I had a couple a while ago and junked two into the garbage after a few uses. Let us know how the usgi mags work for you. By the way, I hope your usgi mags don't say promag on them...

 

[Gator 45/70]

Shoot me a p.m. I have some H&K mag's and P-Mag's that you can use if needed to test out with.

Thermold mags. I have a couple USGI mags ill try in the morning to just for the Hell of it. I'm completely new to ARs so I'm lost.

 

[rrussotwo]

Sounds like the Thermold might be the problem.

NFA lowers come with standard carbine buffers, so that shouldn't be it.

Check it out with a known good mag first.

Second try some 5.56.

Third bring the upper to a smith or some AR guy near you. We have lots on the site.

The worst of the likely stuff is the gas block is not on right or gas key is loose. Both are easy fixes.

What BCG?

 

[Pas Tout La]

Ok I tried it again with a metal Brownell mag and still the same issues. It will eject the round but will not cycle a new one. Even if shooting only one round in the mag the bolt will not hold open. Anybody in Lafayette willing to take a look at it for me? I'm thinking it might be a buffer and spring issue because (I already said I do not have sufficient knowledge with ARs so take it for what it's worth) it seems like its heavy to charge. A lot more resistance than I would expect.

 

[Bam Bam]

Sounds exactly like what happened to me the other day with AR that wasn't lubed good. I pulled the buffer and spring, poured a little oil in my hand and rubbed it on the spring and some inside the buffer tube. Bingo, no more problems! I would lubed the bolt and buffer spring and give it a whirl.




Bam Bam

 

[SpeedRacer]

Throw away the thermolds. Lube the hell out of the BCG. If it still has issues try the upper on another known good lower if possible. That will narrow it down.