Grendel AR not feeding?

[Daddycaddie67]

At the range yesterday with my Grendel every few rounds would hang up and some would cycle correctly. This is the same ammo that I used last year on a prairie dog hunt. I shot 130 rounds over three days with no issues. To me it seems like they aren’t clearing the locking lugs at the chamber.
As you can see by the pics the one on the left has two dents identical to the lugs and the other two are scratched and dented as well. The magazine is an Alexander arms 10 round that I never leave loaded. This morning I loaded up 10 dummy rounds and that all cycled by hand fine. I then ran them through a 20 round Alex magazine and they to cycled fine
Any suggestions?

 

[mac86951]

If you load one in a mag and fire; does the bolt lock open with mag catch on bolt face?

Looks to me like something in your gas system is leaking; or excessive drag in operation, over-gassed can do this too. There are a few things to check and a few sub-systems that can cause it; so you're going to learn a lot about your rifle soon.

Hand cycling is a good rough guess; but you don't hand cycle with the same speed, force, timing as the gas system. Try the above test and let us know. Do you have a patch of black soot around your barrel at the gas block? How does your gas tube fit the gas key on your bolt carrier? And how does your bolt fit the bolt carrier; are the gas rings intact? Is the ejector spring weak?

Apologies, each of these questions can become a thread all in themselves; but in diagnosing the issue; we gotta rule out that the computer is plugged into the wall.

Tangent: when did you last clean your chamber? Chance there's excessive force needed to reject the brass? What loads are you running, what do the case-heads look like, overpressure, case-head swipe?

Ok that's a ton of places to look to start.
-Mac

 

[Daddycaddie67]

Yes, bolt locks open. Definitely not over pressure. The load is in one of the pictures( the 30Gn load is/was a mistake and were pulled before I went to the range. when you mentioned the gas system I remembered the other day the gas tube retaining pin at the gas block was starting to walk out, maybe it came all the way out? ill check when I get home. Thanks for all the suggestions. E

 

[msalm]

Look at your ejector face. It’s the stripping/feeding cycle and my bet is it’s hanging up on the bottom edge of your ejector and jamming between that, the feed ramp, and the top of your chamber (bullet point). The fix is to add a chamfer on the bottom front edge of your ejector.

When the round finally releases from the mag, it’s already angled up on the feed ramp. If you tip a round up and slide it up your bolt face, you’ll see where it catches. It’s not much but a quick rounding/ramp on that bottom edge will fix your problem.

 

[Coyotefurharvester]

If you ever dropped the mag, issues can seem to pop-up. Especially the aluminum mags.

 

[Daddycaddie67]

If you ever dropped the mag, issues can seem to pop-up. Especially the aluminum mags.

Im sure I have. Comparing it side by side w a new one it looks the same.

 

[Daddycaddie67]

So the gas pin is in place and everything looks good w the gas system, at least to my untrained eye. The ejector face is rounded over where its closest to the bolt face, not sure if the pic will show it well enough. Is that normal gas leakage at the gas block?

 

[Walt Krafft]

You mags are for the Grendel and not 223 correct?

 

[SecondsCount]

I would replace/upgrade the recoil spring.

 

[Daddycaddie67]

You mags are for the Grendel and not 223 correct?

Yes

 

[Daddycaddie67]

I would replace/upgrade the recoil spring.

It has a JP silent spring, a couple hundred rounds through it with no issues till now.

 

[Coyotefurharvester]

Extractor/ejector look fine, you could strip the bolt and ultrasound clean and lube(maintance). Gas tube leak is normal, my suppressed fire gas tubes(non adjustable block) get dirtier than your pics. If it shot fine and now not, something you changed or something was damaged/broke. You said you have a new mag, try it. If the gun runs you know it was the mag you dropped. Run a pipe cleaner in the gas tube, and try the old mag before you try the new mag(after the bolt clean/lube).

 

[msalm]

Add a larger chamfer to the bottom front of the ejector (not extractor). I have seen this with multiple AR’s in Grendel. Think of it as a ramp, instead of hanging up on the ejector the base of the round will slip up the bolt face and have a straighter approach into the chamber. Trust me, that’s all you need to do.

 

[Hudge76]

Have you tried shooting it with a different mag? Start with the easiest to rule out which is usually the magazine.

 

[Daddycaddie67]

Have you tried shooting it with a different mag? Start with the easiest to rule out which is usually the magazine.

That’s what I’m planning. Thanks

 

[Klong]

Did you lube the buffer spring?

 

[Daddycaddie67]

No, I’m running a JP silent buffer. Would that matter?
Update: shot it yesterday with a new magazine and same problem, only one shot and put it back in the case. I did notice that the right side feed ramp is a little proud of the upper’s feed ramp. Should I get this polished out?

 

[boltfluter]

Add a larger chamfer to the bottom front of the ejector (not extractor). I have seen this with multiple AR’s in Grendel. Think of it as a ramp, instead of hanging up on the ejector the base of the round will slip up the bolt face and have a straighter approach into the chamber. Trust me, that’s all you need to do.

A pic here may help get the point across. Hard to visualize what you are describing. Just a thought.
Paul

 

[msalm]

A pic here may help get the point across. Hard to visualize what you are describing. Just a thought.
Paul

Grind/polish a slight chamfer here, sloping downward. Basically a ramp that the top edge of the brass will not catch on as it strips out of the mag feed lips. The round is already at an angle from the ramps on the barrel extension and the round gets wedged between the extractor, ramp and the bullet point hitting the barrel face. If the round doesn’t catch on the extractor the base rides up faster and presents a straighter path into the chamber…no wedging. I’ve actually only seen this in the Grendel case where it happened reliably, and then not with every one of them…but enough I’ve had to do this a half dozen times and the problem was solved.

 

[msalm]

On the OP’s bolt pic, you can see where the rim of the case could hang up just enough on the highlighted edge of the ejector enough to keep it down too long. In one of his pics of the cases you can see where it was jammed into the feed ramps with the base low, point up. A chamfer on the red mark will fix his feeding issue. You could even just chuck the ejector into a drill and spin against a file at a light angle then polish, adding a chamfer around the whole ejector. It’s a $2 part, nothing to loose really.