12-11-2017, 03:54 AM (This post was last modified: 12-11-2017, 04:11 AM by 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...
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
Knowing everthing isnt as important as knowing where to find it.
12-11-2017, 03:20 PM (This post was last modified: 12-11-2017, 03:26 PM by VASCAR2.)
What gas block are you using Gos, I assume a fixed gas block as it sounds like a complete upper from JSE. An 18 6.5 Grendel with this type of failure can be over gassed. Many times the symptoms of over gassed and under gassed are the same.
If you have a 5.56/223 PMag you can usually get three to five rounds to reliably feed to maybe eliminate the possible mag failure issue. What type of buffer tube, buffer and buffer spring are you using? If your not using an adjustable gas block and you eliminate the cause as being a mag Id probably buy an adjustable gas block.
If your using a carbine length buffer tube, carbine spring and 3 ounce buffer. Have you tried a heavier H-2 buffer or put the upper on a lower with a rifle length buffer tube, rifle buffer and rifle buffer spring?
12-11-2017, 09:56 PM (This post was last modified: 12-11-2017, 10:07 PM by 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.
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.
"Down the floor, out the door, Go Brandon Go!!!!!"
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.
Try a different mag. Actually try a few different mags. It's the easiest thing to swap and many issues are mag related.
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.
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.
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.
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.
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...
warp9764 Wrote: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%.
What are the components of the lower? Buffer weight and spring ? Have you chronoed the factory vs reloads? That would help determine under gas or over gassed. I would bet it is on the under gased side, your reloads a bit slower then the factory load, and the buffer spring is faster then the mag spring. So heavier buffer, or different mag.
Another thought... full bcg backward travel can be inhibited by new parts not broken in against each other... IDK but you'd get a weak eject then not fully cycled back to fully pick up the next one, so it slides over... kind of short-cycles.
I had one 18"-er that I had to basically feed single feed for the first 40-50 rounds... tried several things but part of it I'm sure was all the new parts being stiff, after breaking in and loosening up they worked better.
I recommend always break in with factory ammo like Hornady 123 Black or Hornady AG123's or the Federal 90's, not too expensive and you have one variable removed from the equation.
$0.02 to consider...
"Down the floor, out the door, Go Brandon Go!!!!!"
This is a gas system/recoil system issue most of the time, when you have Bolt Over Base malfunctions.
It's more common on 18" MLGS AR15s.
Due to the plug dwell time, cyclic rate can be too fast for the magazine to lift the cartridges up fast enough, so the bolt slips past the cartridge, and the carrier tries to drive it forward.
You end up with bolt lug dents on the shoulder of your cartridge usually, with the cartridge beat up pretty bad.
Gotta slow the cyclic rate down somehow. Pick one or a combo of these:
Adjustable gas
Heavier buffer
Heavier spring rate for the action spring
NRA Basic, Pistol, Rifle, Shotgun, RSO
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6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
LRRPF52 Wrote:This is a gas system/recoil system issue most of the time, when you have Bolt Over Base malfunctions.
It's more common on 18" MLGS AR15s.
Due to the plug dwell time, cyclic rate can be too fast for the magazine to lift the cartridges up fast enough, so the bolt slips past the cartridge, and the carrier tries to drive it forward.
You end up with bolt lug dents on the shoulder of your cartridge usually, with the cartridge beat up pretty bad.
Gotta slow the cyclic rate down somehow. Pick one or a combo of these:
Adjustable gas
Heavier buffer
Heavier spring rate for the action spring
Of the above three options, I prefer reducing gas. It softens the impulse, thus reducing felt recoil. In some cases, it even takes the heat off the family dog. Assuming the BCG is of standard weight, my opinion is that heavier buffers or springs are simply treating the symptom, not the cause.
If it's true that we are here to help others, then what exactly are the others here for?
