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Desperately Need help with AR-10 malfunctions


GetAwayDriva

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Big Bertha is going in the trash if we can't get her running properly.  I am having a failure to eject the spent case while trying to feed in a new round.  The rifle is a DPMS with a JP parts consisting of a silent capture spring, gas block, lmos and enhanced bolt.  It has a criterion 20" barrel on it.  No more than 1700 rounds down the barrel and no more than 1500 rounds on the bolt carrier and bolt.  I adjusted the gas to lock open after shooting the last round out of the mag.  Had the jams.  Gave it more gas.  Still had jams.  Picture included shows a typical jam.  (Gonna have to continue this in another post since it won't allow me to upload another picture)

IMG_2896.JPG

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I had a couple guys look at my bolt/extractor/ejector at Heman and they thought there was enough tension in those parts to do the job.  I would hope you could get more than 1000 rounds on an extractor/ejector before they went tits up.

 

 

We happened upon a YouTube video showing a malfunction where the spent case was flipping back into the chamber so I got to looking at my receiver and noticed a good ding on my brass deflector and the edge of the port was all chewed up as well.  (Notice the goldish discoloration on the edge of the port near the deflector).  I compared this to my husband's rifle and his had a tiny grey mark where the top arrow is but that was it, nothing in the port where the lower arrow is pointing.  His brass deflector did not have a sharp edge like mine.  So wondering if the spent case was hitting things and flipping back in, We dremeled on it to remove the sharp edge and put a slight radius on the port edge. Well that didn't help either.  

 

Our load is a minimum charge (don't know how much) of 4064 behind a 168 gr bullet, going 2489 fps,  but it has done this with factory ammo (perfecta stuff from Walmart) as well.  

IMG_2875.JPG

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It has been doing this off and on throughout the time since I put in the lmos and new bolt, roughly 1500 rounds. At Heman, for example, it did it twice per stage on 4 of the 6 rifle stages.  We started adding gas after the first stage it did it on, thinking perhaps I was under gassed.  That didn't help so we put it back where it was.  It does lock open when you shoot the last round out of the mag, for what that is worth.  

Edited by GetAwayDriva
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Dianna, you know I was having similar issues with my rifle at He Man. I opened the gas up, bolt locked back every time, even when it was cold. Locked back prior to opening up the gas too. Prior to the match, I removed my DPMS bolt carrier that I had put an adjustable gas key on, and put in a brand new Rubber City Armory bolt carrier group. Saturday, after we were done shooting, with much frustration, and lots of desperation, I put a JP bolt into the carrier. Tension was much less between the bolt and carrier. Jim Lambert thought it was too loose, I didn't care. Personally, I'd rather have it loose than too tight. Went back to the sight in range, and dumped a full mag out of the gun. Brass was ejecting to a normal distance. The gun ran perfectly on stages 5, 6 and 7 Sunday morning. I'd try polishing the gas rings with some 400 wet or dry, lube it good, and see how it runs.

As to the brass flipping back into the port, was the case head out of the port and the neck inside?

Edited by Dan Sierpina
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My 308 had a very narrow window of operation with low mass parts, like 1/8th of a turn one way or the other on the JP adjustable block and it would stop running.  Back to the standard 308 carrier from DPMS and presto, rifle runs like a scalded dog.  

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3 hours ago, 1chota said:

JP told me to set the gas where the empties eject to the 3-5 O'clock position. 

I think you are cursed and you should sell me your rifle for $50.  (LOL)

Haha!  I just may do that......

 

Rounds landing at the 2 o'clock position.  I did give it more gas and it didnt help.  Bumped it up a quarter turn right before Heman.  Still did it.  Bumped it up another quarter turn at Heman.  It still did it. 

Edited by GetAwayDriva
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It is currently getting just enough gas to lock back.  I adjusted up in 1/8th increments till it locked back.  I did that yesterday.  This morning when I went out, it wouldn't lock back so I gave it another 1/8th turn and it locked back.  It is not getting too much gas.  Rounds land at the 2 o clock position.

Edited by GetAwayDriva
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My AR10 (Armalite) developed a similar issue. It is a 20" rifle gas, non adjustable gasblock, full weight carrier gun with a JP recoil spring (rifle length buffer). It ran for 4-5 thousand rounds flawlessly before it started acting up. It turned out to be a broken ejector, it had just enough material left on it so that it wouldn't fly out of the bolt, but would bind and not push the case all of the way out of the rifle sometimes. I had strike marks on the front end of the ejection port from case mouths getting knocked into it. Most of the time, mine would leave the case sticking out of the ejection port in stovepipe fashion. It has been good since I replaced the ejector. If you have another rifle at your disposal, try swapping the bolt (or other parts, one at the time) and see if it makes a difference.

Hurley 

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Your bolt/BCG is accelerating forward to fast,  for now remove the low mass bcg and replace it with a full mas then see how it does. Or replace the silent capture spring with a normal spring and buffer.

Edited by DocMedic
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I had a similar issue with a DPMS barrel... found out that the C/L of the barrel was offset from the C/L of the Bolt.  Swapped out the barrel and the problem was solved.  Still trying to figure out how to re-align the barrel, because it shoots less than 1/2 MOA with just about anything I put into it.  

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Thanks every for the replies.  So I traded out bolt/carrier with the husbands today (thank you Hurley, that was a wise idea) and same problem.  So it is definitely not extractor/ejector.  I backed off gas enough to where it wouldn't always feed the next round out of the mag, let alone lock back, but the cases did eject.  I also tried giving it way too much gas just for knowledge, and that didn't work either.  So next test is what DocMedic suggested and we will see what happens there. 

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2 hours ago, Rookie said:

I had a similar issue with a DPMS barrel... found out that the C/L of the barrel was offset from the C/L of the Bolt.  Swapped out the barrel and the problem was solved.  Still trying to figure out how to re-align the barrel, because it shoots less than 1/2 MOA with just about anything I put into it.  

How did you determine that the C/L of the barrel was offset?

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My Gunsmith took the time to take some measurements while trying to identify the problem.  I don't recall the amount that it was off and can only confirm that swapping out the barrel was the only change I made and the problem went away.

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Had same thing happen working up loads with new gun.  Make sure you have two rubber doughnuts under extractor. What can happen is there is not enough tension and ejector knocks case out of extractor before it clears ejection port.  Gun will still lock back as if this is the issue gas is not the problem. 

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ditch the silent captured spring--mine developed hiccups with it.  I am back to the JP regular spring.

also, I changed to a new spring this year, after 5000 rounds I thought it a good thing. (??)

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After a phone call to JP, we may have a solution.  the gen 1 SCS used stainless weights. The new version (H2 ?) Uses tungsten weights.  Confirmed with scale we do indeed have the gen 1 SCS.  Apparently the lighter weight SCS gives a very narrow operating window.  Luckily they do offer the tungsten weights separately.  As soon as they arrive I will report back.

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On 5/25/2017 at 2:32 PM, 1chota said:

did this just start?

 

lots of variables here.

 

please elucidate.

 "elucidate"    damn, I like that word.   Had to look it up!!

 

thanks for that...

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On ‎5‎/‎31‎/‎2017 at 11:47 PM, busdriver said:

After a phone call to JP, we may have a solution.  the gen 1 SCS used stainless weights. The new version (H2 ?) Uses tungsten weights.  Confirmed with scale we do indeed have the gen 1 SCS.  Apparently the lighter weight SCS gives a very narrow operating window.  Luckily they do offer the tungsten weights separately.  As soon as they arrive I will report back.

+1 on this, I had a Gen 1 SCS in my AR10 and had nothing but problems.  Not the same problem as the original poster, mine was failure to fully chamber the next round.  Switched to the Gen 2 with the heaviest spring they offer, upped the gas, and gun runs much better.  Good luck.

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