Looking for an AR-15 expert, intermittent feed issue

[Winkfish]

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,

 

[cohunt]

Try a different brand of mag-- sounds like it could be a mag issue

I've had good luck with asc ss mags (sometimes need to tweak lips though ) with other cartridges in ar15 platform

 

[Orange Dust]

Try opening the gas port a little more. I set mine 1/2 turn past lockback.

 

[Winkfish]

I have tried 2 brands and a total of 6 magazines. This is all I could get my hands on right now. The problem does occur on all 6 magazines.

CMMG 10 and 15 round (2, 10 round, 1 15 round)
ASC 10 and 15 round. (2, 10 round, 1 15 round)

 

[Winkfish]

I have tried tried almost every position on the gas block as well trying to tune it with multiple rounds with everything from wide open to nearly fully closed where it will not unlock.

 

[cohunt]

If you open the gb all the way-- where does your brass eject to??

Have you tweaked the lips on the mags to make sure they feed the ammo nose up-- not nose parallel?

 

[Orange Dust]

Is the bolt one of ARP's Superbolts?

 

[tbird86]

Sounds like higher mag spring pressure is hampering forward bolt travel. If more gas (higher bolt velocity) doesn't solve it, I'd try switching the buffer setup to something that uses a rifle-length spring -- either A5 or rifle.

 

[SPitty]

Have you tried a lighter buffer?

 

[Winkfish]

The bolt Carrier is a Aero and Midwest industries.

I did try a rifle length spring with the same issue.

I have not tried a lighter buffer. I was (maybe wrongly thinking that adjusting the gas would help drive that carrier back)

Below two magazine that are currently loaded with 10 rounds each of factory ammo.

 

[cohunt]

Adjust lips so nose of bullet is up-- may not fix the problem but it definitely won't hurt it either.

When you put more rounds in mag- pressure on ammo is greater against lips and can cause misfeeds, bolt jump over, or bolt to not cycle correctly.
If you adjust feed ramps so bullet is more nose up then it eases the force that it takes to load the bullet, also the nose doesn't hit the feed ramp.

Your loaded mags look like my top picture example-- tweak the lips until the bullet noses up to look more like my bottom pic

Try tweaking the lips in one of the mags and see if it helps at all


When the gas block is all the way open? Where does your brass eject?

 

[Orange Dust]

Sounds like higher mag spring pressure is hampering forward bolt travel. If more gas (higher bolt velocity) doesn't solve it, I'd try switching the buffer setup to something that uses a rifle-length spring -- either A5 or rifle.

You and I are thinking the same. He tried a different spring. I asked about increasing gas and a superbolt (less Drag). All that is left is the buffer. Lighter will increase bolt velocity. I still think the gas is too low for the load.

 

[Old Rooster]

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/

 

[Orange Dust]

What happens if you just drop a bolt on a full mag from lockback? What happens if you cycle the bolt? The bolt should go completely into battery. If it doesn't I would look at the magazine.