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AR jamming only when it's clean

L

lennyo3034

Gunny Sergeant
Full Member
Minuteman
Apr 18, 2010
3,066
932
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USA
I'm trying to resolve an issue with an AR. It is failing to eject, and stovepiping, but only after the bolt is cleaned. The first 2-3 rounds will, and then the rifle will be good to go until the bolt gets cleaned again. Aside from the obvious "don't clean it", does anyone have an idea on what could be happening?

Jamming occurs with both heavy lube and light lube. Also occurs when whole rifle is cleaned, or just the bolt. So far its only been shot with LC M855, but if we don't clean it, it will go 1000+ rounds without a hiccup. Rifle shoots accurately and very softly, locks bolt back on brass cased ammo 100% of the time. We've run a couple boxes of Tula through it and it does not always lock back on the last round. This makes me believe it is not overgassed.

Ejection is very weak, brass only going about a foot or two at 1:30-2:00. This makes me believe it could be a ejector/extractor spring issue. The extractor seems to be strong enough, the ejector spring feels a little light when I push on it. However this theory does not explain why it only occurs when clean.

My other thought is the gas rings. They don't look the best, but not terrible either. I always lube them when I clean and they seem to seal well enough. Bolt stays in carrier when help upside down. However it's possible the rings are tight, but gas is leaking through. I didn't think that would cause a failure though as some rifles have run on one ring.

Anyone have a clue what could be happening? This is a friend's rifle, and we are going to replace the extractor and ejector springs first. Not sure where to go from there.
 
It's a bit of a frankengun. And by "bit" I mean VERY. It uses an SR-15e3 barrel extension and bolt. I don't have another one to swap in. I did order new springs for the bolt to try though. The extractor still looks good and is sharp.
 
Compared to my standard bolts the ejector plunger is not as stiff. I have ordered a tubb extra power ejector spring. That can explain weak ejection, but not why only first rounds.
 
My shorty used to do this; mainly because lube would get in the gas tube and inhibit the gas flow until it finally blew it out or burned it off. I'm careful now when cleaning the bore, to blow the gas tube clear with a compressed air hose or can of compressed air...haven't had problems since...

JMTCW...
 
Make sure the chamber is dry---no lube.

I have 1 AR15 that eats the standard gas rings alive. It never malfunctioned but when I pull it apart after 100 rds or so there are pieces of gas ring missing. I never found the missing pieces, and after about the 3rd set of rings I put in a McFarland 1-piece ring and have never had another problem. The moral of this story is that I no longer believe that lining up the ring grooves has much effect on gun function unless it's already undergassed for some other reason. 2 out of 3 gas rings in mine had like 1/8" gaps and I never knew there was a problem until I cleaned it. Since that experience though, I have installed McFarlands in all my AR's. All the Armalites I've seen came with McFarlands as well. I'm not trying to sell anyone on the 1-piece gas rings--just reporting my experiences. Like I said, I really don't think the gas rings have to seal that well unless the gun is undergassed to begin with.

It does sound like the ejector spring is weak, and a totally clean/lubricated bolt may possibly move just a tad faster---not giving the weak spring enough time to properly eject the empty case.

I'm no expert by any means but I've done a lot of tinkering/troubleshooting on my POS AR15's and I have stayed at a Holiday Inn Express once or twice. I installed Wolff extra power springs on all my 16" carbines--extractor, ejector, and buffer springs. Once again-MY AR'S ARE POS's, YMMV
 
Thanks, that makes a lot of sense. Yes...if anything this rifle is undergassed. It does not always lock the bolt back on Tula in it current configuration. I don't use Russian ammo, so I went with this for the softer recoil. The gas rings have survived at least 1000 rounds, but are looking a little worse for wear compared to some of my other rifles now. The Mcfarland's are on my radar, as are the equivelent JP enhanced rings.

I will be replacing the ejector spring with an extra power one and see what happens. I'll probably swap out the rings too.
 
Usually just a boresnake and CLP. Sometimes not at all. Whether I clean the bore or not has not had an effect on the first few rounds.
 
Stop cleaning, Just keep lubing. If your not getting malfunctions or other issues, there is no reason to clean the gun. Carbon will help the gun run a bit better, as long as there is lube.

Boresnakes are a waste of money. Shoot the barrel until it starts to group poorly. More damage is done by over cleaning and improper cleaning than anything else.

The question is, where did you get the gun E3 extensions are not sold on their own? Who built it?
 
OP,

Troubleshooting a problem like yours, headspace (cartridge or chamber) is one possible cause for short cycling. In your instance, upon cleaning insufficiently with the bore snake and CLP, the residue from the Tula cases is being concentrated at the chamber's shoulder, effectively creating insufficient headspace causing the first couple of rounds chambered after cleaning to stick in the chamber. Since the extractor must pull the stuck casing out of the chamber goo produced by the case reside crude and CLP located in the shoulder area, this results in short cycling. Before you do any parts replacement, clean your bore with something like Gunslick Foam Bore Cleaner, letting it remain in the bore overnight. Using a bore guide and one piece rod patch the bore with an appropriate patch wrapped on a jag. Stop shooting the Tula ammunition. Now if the Tula ammunition has nothing to do with it, the problem is simply insufficient cleaning, powder residue and CLP being concentrated at the shoulder causing insufficient headspace thus cases sticking in chamber. Again, the bore snake is not getting out the goo, just concentrating it at the chamber's shoulder. The reason things clear up is that with each firing the goo is burnt off.
 
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I will try that, although I don't usually shoot Tula. I've fired 40 rounds of it total, and it's been around 300 rounds since I last shot it. I have some gunslick at home and will treat it after the range today.
 
Is it possible that there is a problem with your gas key? Maybe a broken hex screw that causes the key to be just loose enough to let some gas escape until the hairline gap is filled with carbon? Just a thought.
 
bowslngr said:
Is it possible that there is a problem with your gas key? Maybe a broken hex screw that causes the key to be just loose enough to let some gas escape until the hairline gap is filled with carbon? Just a thought.
Click to expand...

A loose carrier key does not present the symptoms associated with the OP's problem. A loose key will cause progressively worse short cycling from an initially lubricated condition.
 
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I agree with a little bit of what everyone is saying. First, i would never over lube an M4/m16. It gets all over everything and gets all over the brass as it chambers and extracts and I never thought about the head spacing issue from it but I guess it makes sense. I had more experience with the excessive lube picking up lots of dirt and carbon and making more of an issue that way. I usually only put a little lubeon the sides of the bolt carrier where the bolts slides.

It sounds like cleaning is also an issue here, if not the entire issue. If youre having problems only after cleaning, then its pretty obvious where to start first. Ill wipe off my bolt but I never clean the barrel till it really needs it. Also, never use a fucking bore snake. All that does is smear shit around and re contaminate your gun with old shit from previous cleanings and probably pushing some into you gas tube. Degrees your chamber and gas tube and use an air compressor to finish the job. Air compressor is great at clearing all your cleaner and extra residue.

For trouble shooting, I always start with the cheapest first and it usually turns out it is something I was doing wrong
 
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It sure sounds like something in the cleaning procedure. Could be:

1. Plugged or obstructed gas port (bore snakes do this, crappy ammo, flushing the receiver crap down the bore, etc.) or tube.
2. Improper cleaning of carrier or bolt leaving debris in the gas key, or even on the gas rings or in the carrier itself. I see this some when people use the US to clean an complete BCG. The crud gets freed up, but never leaves the carrier.
3. Crap on the bolt lugs or in the barrel extension.

Whatever you do, DO NOT leave foaming bore cleaner in the bore overnight. 30 minutes max!
 
This happens when i only clean the bolt and not touch the bore. I just switched to a mcfarland gas ring, will see what happens. So far this has everyone stumped.
 
Seems the mcfarland rings are doing the trick. Will go home ans clean again and see if it jams this afternoon.
 
Yeah, I haven't heard great things. I'll keep a lookout on it. I'm planning on getting out to the range one more time today. Waiting on the mailman to drop off a bolt assembly tool so I can put a new ejector spring in. Hopefully he'll bring my new comp too.
 
Solved! So it appeared I had a combination of factors: slightly undergassed, leaky rings, and weak ejector spring. I replaced the rings with a Mcfarland one piece, cannibalized an ejector spring from a spare bolt, and swapped a standard carbine buffer spring instead of a sprinco blue.

It ran perfect, with strong ejection at 4 o'clock. No dings on brass from hitting rear of ejection port.
 
lennyo3034 said:
Solved! So it appeared I had a combination of factors: slightly undergassed, leaky rings, and weak ejector spring. I replaced the rings with a Mcfarland one piece, cannibalized an ejector spring from a spare bolt, and swapped a standard carbine buffer spring instead of a sprinco blue.

It ran perfect, with strong ejection at 4 o'clock. No dings on brass from hitting rear of ejection port.
Click to expand...

Good news. Just remember the 1 pc ring does not have to be as tight a fit as the std 3 rings, so with use it will likely fail the test of holding the weight of the carrier when stood up on the bolt face. I assume the sprinco blue is a heavier buffer spring?
 
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JP makes a one piece gas ring now...... I've never had any issue with McFarland rings though... From my understanding there were some cheap knock off being sold as McFarland gas rings that were out of spec causing the issues you read about so it's important to order them from a reputable source.... I just switched to the JP's in both my AR15's and 308's.
 
Took it to the range again today. Ran perfectly except did not lock back on super low powered reloads. Not surprising considering the rifle setup.

Here is the Rifle:

DSC01791_zpsf0d0834d.jpg


Colt 6920 Lower with ambi controls and Geissele
Colt upper receiver
SLR rifleworks handguard
KAC 16" SR-15e3 barrel
KAC SR-15e3 bolt
KAC intermediate length gas system
KAC buffer (carbine)
Sprinco white buffer spring

Basically someone parted out a KAC upper and I picked up the internals to put in my build. Now that the parts are replaced, it runs great with extremely light kick. I shot it next to a midlength with a rifle buffer yesterday, and it was noticeably softer shooting.
 
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