Looking for an AR-15 expert, intermittent feed issue

[BigDon]

I read a while back that the 6mm ARC had feeding problems and there was one magazine brand that did not have that problem.I wish I could remember which one it was because i haven't gotten around to building mine yet. I'll have to see if I can find that article.

Alexander Arms

 

[Teri Anne]

Good Morning, I am wondering if any of you AR-15 experts can help me out with an issue I am having.

Here are the Gun Spec:
6mm ARC, Factory ammo 108gr ELDM or handloads @ (108gr ELDX, BR4 primer, leverrevolution, at 2,732 fps)
Bartline 24" barrel 1:7 twist
Triggertec Diamond 2 stage trigger
Carbine length buffer with a standard 3 oz buffer
6.5 Grendal bolt Gen 2 verified with face depth measurement
Tried both standard spring and +15% power wolf spring
Superlative arms adjustable gas block. Rifle +2" gas system .092" gas port
CMMG and ASC metal magazine both 10 and 15 round

So here is what is going on.
Start with the gas block turned out about 4.5 turns per factory specs.
Place a round in the magazine. it fires and the bolt locks open. I clean the barrel and repeat. I work my way up to 3-5 shot groups and repeat. Everything cycles fine and the guns shoot well. Shoot 5 shot strings to 100 rounds. At this point I have not shot the gun with more than 5 rounds in the magazines.

Then I do load development on some ELDX and Leverrevolution powder. Shooting 3-5 shot groups it works just fine. This is across 6 different magazines all 10-15 rounders.

Now I am around 200 rounds down the tube.

This gun is setup for PRS and is going to be my daughters gun for this season. Now we are going to try and run a normal 10 shot stage. start shooting the gun. around shots 5-7 I wiLl get a failure for the bolt to lockup up / go into battery. In some cases I am able to hit the forward assist and close it, then fire the gun. Other times the round is not far enough out of the magazine to allow that to happen. In some cases it is close to going into battery and when you pull the trigger it just goes click. If I drop the magazine, I am able to pull the charging handle, let it fly and it locks up. I am then able to pull the trigger and the round goes off.

If I single feed, no issues. if I put 3-5 rounds in a magazine no issue. This testing is being done on the factory ammo and not the reloads.

I have played with the gas system and dialed it in so that it is cycling fine and putting the brass at about the 4-5 O-clock position in a nice little pile.

I have tried different buffer springs to see if a stiffer spring would aid in lockup but it has not. I went to a different bolt carrier group and tried that on both springs and that didn't help either.

I am into this about 500 rounds now and I am unable to get it to run a full 10 rounds without a failure. This is starting to get a little expensive to figure out.

This problem will occur on reloads and factory ammo.

If anyone has any suggestions please let me know, I am at a loss and not sure what to do next.

Thank you,

I have a lot of experience with the AR-15 both in combat and competition. The bolt failing to LOCK UP is not usually magazine related. To me it sounds like your bolt is improperly lubricated and binding up when trying to lock up. What I have experienced is that new modern synthetic lubricants do not have enough body to remain in place causing the lock up to bind due to lack of lubrication after a few shots. Try a heavier grade of lubricant, Military grade CLP or some LSA that is a bit heavier and hangs on the metallic parts. That might solve your problem.

 

[Coyote Shadow Tracker]

Buffer tube may be at fault but as cohunt said the bullet tips should be upward and not parallel.
There is a tool that works great but I have done most with a pair of pliers.
That fixed my problems on 2 different ar15's.
Here is that tool https://masterpiecearms.com/shop/mpa-mag-feed-lip-adjustment-tool/

You can also make a "Feed Lip Tool" with an old screw driver with a thick shank. Grind the tip off then cut a slot into the shank with a hacksaw or Dremel cutting wheel. Look at Brownell's for the one they sell and just copy. I made one many years ago. (easy to make).
Len & Jill

 

[chav0_12]

Alexander Arms

Yeah, I'd have to agree. For my Grendel anyway. I have an ASC and was having similar problems to these, bought an Alexander and no feeding issues since.

 

[Winkfish]

Interesting to note that on Alexander Arms website: https://www.shopalexanderarms.com/6_5_Grendel-Magazines.html

They have the following Note:
It has come to our attention that some reseller are marketing the Alexander Arms 6.5 Grendel magazine as being compatible with the 6MM ARC cartridge. This is not the case, the AArms 6.5 Grendel magazine is optimized specifically for the 6.5 Grendel cartridges only, it is not optimized for the 6MM ARC and our experience is that the 6MM ARC cartridge will not reliably feed from the 6.5 Grendel magazine. If/when Alexander Arms begins to market a magazine for the 6MM ARC cartridge the magazine will be so marked.


I believe you when you say it works,

I now have 6 magazines that are CMMG and ASC that I have "Modified" the lips on and are now working as I need. I would like to try a poly mag and some of the other ones mentioned to gain some additional info based on my application

 

[BigDon]

Interesting to note that on Alexander Arms website: https://www.shopalexanderarms.com/6_5_Grendel-Magazines.html

They have the following Note:
It has come to our attention that some reseller are marketing the Alexander Arms 6.5 Grendel magazine as being compatible with the 6MM ARC cartridge. This is not the case, the AArms 6.5 Grendel magazine is optimized specifically for the 6.5 Grendel cartridges only, it is not optimized for the 6MM ARC and our experience is that the 6MM ARC cartridge will not reliably feed from the 6.5 Grendel magazine. If/when Alexander Arms begins to market a magazine for the 6MM ARC cartridge the magazine will be so marked.


I believe you when you say it works,

I now have 6 magazines that are CMMG and ASC that I have "Modified" the lips on and are now working as I need. I would like to try a poly mag and some of the other ones mentioned to gain some additional info based on my application

This true. However Alexander has 6Arc-specific mags.