Failure to Feed Issue

[Pr589]

Shooting a buddy's AR today and was having failures to feed after 2 or 3 rounds. Would like your thoughts on what might be the cause and the cure.

The gun is a Noveske AR in 223 that has run problem-free up to this point (hundreds of rounds). The failure usually occurs after the second round when the third round is loading. The third round is partially stripped from the mag then becomes jammed, projectile-up at a 30-45 degree angle, between the bolt and feed ramps. This usually leaves a dent in the case where the bolt has pressed against the round.

We tried multiple mags, all of which have worked flawlessly prior to the problems, with no success. The ammo was factory loaded Lapua 223. The first and second rounds cycle normally. When the FTF is cleared, the rifle will run normally for a few rounds before experiencing another FTF.

Thoughts?

 

[CraigNConnor]

Do you normally shoot lapua ammo through it ?

Try differant ammo

Is the stuff you were firing hollowpoints?

 

[CraigNConnor]

Has the gas tube been cleaned ever?

I know if I slowly rack my action I get failures like this ( let the bolt go forward stripping a round off the mag slowly it will point up and fault to chamber

If your bolt is not traveling as far rearward as possible (maybe the BCG is traveling back just far enough to strip a round but not pick up enough momentum for a fast hard chambering due to not getting full gas.

Thoughts? Anyone else

 

[Sinasta]

You dont need to clean the gas tube.

 

[jakester]

I would check the gas rings on the bolt to make sure the gaps on all three rings are oriented away from each other. The problem you're having is sometimes the result when the gaps are all lined up...

 

[Chrossphyre]

Definitely sounds like a lack of gas/slow bolt problem. Check bolt seals, gas system (partial obstruction?) and bolt path/ramps.

 

[beltfed]

Sounds to me like it is short stroking - but anything at this point is a guess. You'll need to diagnose it further. I'd Clean with a detailed strip and scrub the chamber really well, lube it up and try again. Bring along some different ammo and different mags for the next outing to help with that.

The gas tube and alignment of the gaps in the rings should not be sources of the issue.

 

[Runningfool]

I would check the gas rings on the bolt to make sure the gaps on all three rings are oriented away from each other. The problem you're having is sometimes the result when the gaps are all lined up...

Nope. That is a myth.

 

[jakester]

It wasn't a myth on mine. The gas rings were well worn, the gaps all lined up, and it short stroked every now and then causing a jam very much the same as the OP's. Not all AR rifles behave the same...

Anyways, It's difficult to diagnose most function problems over the internet, really needs to done at the range.

 

[Pr589]

Thanks for the response folks. My thinking was mag/feed-lip issues or short-stroking however our testing at the range seemed to have eliminated mag issues as the problem (we tried 5 different mags which worked prior), leaving gas issues as the default. I admit I'm at a loss as to what could have suddenly started causing gas issues - DI systems are so simple. We're now down to trying low-probability causes like gas-ring alignment and gas-tube obstruction.

The rifle is relatively new with more than 500 rounds but less than 1,000 down the pipe so wear (bolt seals, etc.) should not be an issue.

Do you normally shoot lapua ammo through it ? Try differant ammo
Is the stuff you were firing hollowpoints?

Have tried numerous types of ammo including HP match and FMJ. In the past the rifle would eat anything but since the onset of problems, it seems any ammo has the same issue.

 

[b_w.]

Dump some lube in it and see if that helps.