FTF On Grendel Suggestions

[Gos]

Greetings,
Sorry to bother everyone, but I'm running out of ideas.
I have a one out of four chance at any given time of having a failure to feed issued on my 6.5Grendel. At first, I thought it was the sharp edge on the entrance to the chamber. The barrel was removed and a very Smoooothly polished radius was applied. It lessened the chances of jamming a lot, but did not fully eliminate the problem. The bolt travels back far enough to hold open after the last shot, so it's not short stroking as it were.

The jam happens by the bolt traveling over the top of the case, pushing the cartridge down and against the barrel extension denting the case badly and of course not cambering the round. I'm hoping my attempt at downloading a picture link will work so you can see exactly what I'm up against. I've been tinkering with this for over a year now and am ready to either sell it or part it out for another project.

The gun is a JSE upper, 18" heavy barrel, later with zero point fluting. The problem existed before the fluting, so it's not like something got put together wrong after the fluting.
The magazines are AR Stoner with 6.5 blue followers.
Ammo Hornady 123 SST.
Problems are bad with factory ammo, and very bad with reloads.

What thinks you all?

My attempts at loading a picture have not yet been successful. Sorry...

[Drillboss]

Are you for sure locking back on the face of the bolt, or possibly on the bolt carrier?

I'm seeing some failure to eject with reloads on a new build, so I'm watching this thread.

[rabiddawg]

The only time one of mine has done this I thought it was locking back too, but the mag wouldn’t fall. That’s when I realized it wasn’t traveling far enough back to catch on the bolt catch ie under gassed.

The only leakage I found was around the gas block. I installed a new adj gas block and cured my problem

[Sticks]

All of the above, and have you tried a different mfg magazine?

[VASCAR2]

[LRRPF52]

Try a different magazine with a more powerful spring, or replace the spring in the current magazine.

If your cyclic rate is on the fast side, it will sometimes beat the mag spring's ability to lift the cartridge stack.

[65Whelen]

I agree with the magazine theory. I just went through the same issue with two new C-Product mags I got from Brownells. The blue mag follower wouldn't level, the back of the shell would dip down just a fraction but enough where the bolt would ride over the top of the shell and jam instead of picking it up and out into the chamber.

I was at the range today function testing 11 new Elander Mags from AA, they have white follower, not one hickup out of 11 mags and three different Grendels.

Try Elander Mags. I see Brownells is now carrying them also try AA.

[TKO]

Heavier buffer will slow down the BCG allowing mag spring more time to push up the next round and have more momentum to chamber the new cartridge.

Solved my issues. YMMV.

[grayfox]

Heavier buffer (Spike T2) and the JP centerless spring helped me out. But the mag thing could also help.
I haven't had any problems with the blue follower, ASC (I think) 10-rounders but that's not to say some others might be problematic.

[Gos]

Wouldn't a slow motion camera be slick for these sort of issues!

[Old dog new tricks]

Check ejector pin length, if it's sticks out beyond bolt lugs it will not feed reliably

[Frontier Gear]

Just my troubleshooting steps and experience.

1. Clean the rifle. Sounds obvious, but it does make a difference. About 80% of the guns that come to me for repair (not just ARs) are simply dirty. A good clean and lube and the rifle functions correctly. About half of the ones that are actually broken, I can trace the failure back to a lack of maintenance.
2. Try a different mag. Actually try a few different mags. It's the easiest thing to swap and many issues are mag related.
3. Try different ammo. I had a shipment of faulty .223 ammo once. About every 5th to 10th round was bad. They would fire but not cycle the bolt fully. Talk about a pain in the butt to figure out. It did it in any gun. Swapping ammo resolved the problem.
4. Swap lowers. It is really easy to do. See if the problem follows the lower or the upper. I had a batch of mis-marked buffer springs once. They were supposed to be standard AR15 carbine springs but they weren't. This helped me find the issue.
5. Inspect the gas block. This is especially true for home builds. Mis-aligned gas blocks, gas leakage and poor quality import gas blocks are the second most common area of problems that I find.

The above steps will usually solve most issues. After that I would swap out the BCG. Again it's very easy to do if you have a spare.

I've tried multiple length gas systems at extreme temperatures in different barrel lengths and different types of factory ammo. The hardest ones that I've found to tune are subsonic 300 blackout pistols. Typically I can get an AR to function correctly with factory ammo by using a quality non-adjustable gas block and standard buffer weights and springs just by eliminating any faulty parts or correcting any assembly issues. While changing buffer weights and springs may solve an issue, it makes me wonder if it is actually covering up a problem (assuming you are using factory ammo). I can see changing buffers and springs for a specific load or a specific use (suppressors, competition, etc...), but off the shelf ammo should run with standard parts.

[sneaky one]

Check the spot where the bullet tip hits the -feedramp on the bbl ext. Either slowly release the bolt , like slow motion, or put a tiny drop of -paint or wifes nail polish, have an extra set of eyes if doing slow mo- cell fone cam works with free slo mo app. Adjust feed lips up as needed with a small crescent wrench--- tiny tiny increments , until center of ramp is hit, or slightly above center.

[warp9764]

Watching! I finally shot my new build yesterday, and my first FTF was _exactly_ like the first photo on this thread. I have an adjustable gas block, T1 Spike's buffer, mid-length gas system on an 18" AA barrel. Started with a heavier spring, went to a lighter spring, then tried a little more gas and now I have a round jammed in the chamber so hard I can't pull it out. I'll start my own thread on that one, but I have essentially the same issue and I'd want to see your resolution.

I'll try dialing back the gas instead, and I'll see about trying a Spike's T2 instead of my T1...

[Gos]

Watching! I finally shot my new build yesterday, and my first FTF was _exactly_ like the first photo on this thread. I have an adjustable gas block, T1 Spike's buffer, mid-length gas system on an 18" AA barrel. Started with a heavier spring, went to a lighter spring, then tried a little more gas and now I have a round jammed in the chamber so hard I can't pull it out. I'll start my own thread on that one, but I have essentially the same issue and I'd want to see your resolution.

I'll try dialing back the gas instead, and I'll see about trying a Spike's T2 instead of my T1...

Wish I had some good information for you, but I'm still not running at 100%.