AR not running

[ToddM]

Figured you semi-auto guys might have some ideas for trouble shooting an AR that isn't running. It's my first AR "issue" and maybe I'm missing something obvious.

When I first got it (S&W MP15T) it ran everything no issues, wolf, winchester white box, american eagle etc. no hiccups with both the factory mags, magpul mags, NHMTG, Cprod, D&H etc. Probably the first 750-1000 rounds no issues. I honestly had not shot it since probably a few months. Took it out to the range this week and it seems like it's short stroking, it's not picking up a round every 5-6 rounds through a mag and a couple times it has not held the bolt open on the last round. So I read up on a couple AR15 cleaning posts and cleaned it as well as I could, carbon deposits everything, oil lubed it really well. Took it back out to the range today, same problems across mags and ammo.

Once and awhile it will shove a round at a high angle into the top of the chamber and jam that way, and when I inspected those rounds it looked like the bolt was catching the case right at or just after the case rim because it would be gouged from that rim up the casing.

It's stock except for an ACE stock, Geissele trigger, eotech, ergo grip and a badger handle latch. Previously it was running okay with all of those items the only new one since it was reliable was the trigger.

In fact I got so fed up with it today I brought an old buffer/spring combo with and cut about 1" off the spring and shaved about 1/8" off the buffer pad just to try and force it to run, same problem.

When it does run it seems like the ejected cases are getting tossed well clear of the gun, as normal. Could there be something that would impact the height of the magazine causing it to sit too low?

I'm going to swap the stock for the factory recoil tube/stock and also change to the factory trigger just to see if that helps.

Thanks in advance!

 

[redirt78]

Re: AR not running

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ToddM</div><div class="ubbcode-body">It's stock except for an ACE stock, Geissele trigger, eotech, ergo grip and a badger handle latch. <span style="font-weight: bold">Previously it was running okay with all of those items the only new one since it was reliable was the trigger.</span>
</div></div>

The trigger shouldn't have anything to do with it short stroking. If it ran fine with all of the parts that are on it then sat for a few months and now it short strokes maybe it's something that could wear out over time like springs, the mag or its just dirty, clogged gas holes/tubes... Something like that.

I see you said you cleaned and lubed it good so maybe going back to the old stock buffer tube, buffer and spring will tell you something. Sometimes when the carrier won't lock back it's because the buffer is too long or the spring has too many coils but you also said you shaved some off of an old buffer and cut coils off of a spring...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ToddM</div><div class="ubbcode-body">I'm going to swap the stock for the factory recoil tube/stock just to see if that helps. </div></div>
Can't hurt ^
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ToddM</div><div class="ubbcode-body">Could there be something that would impact the height of the magazine causing it to sit too low? </div></div>
Try a new magazine, maybe the feed lips or the spring in the mag is wore out.

 

[ToddM]

Re: AR not running

Yeah I didn't figure the trigger would cause it, especially since it's not binding/stiff when running the bolt etc. Just figured I'd swap everything out to stock and see if it runs at this point.

That's not a bad idea, most of the mags I took with have sat around loaded over those months, next time I go out I'll make sure to drag some new ones magpul and milspec mags with.

Aside for cleaning out the bolt carrier group, and running a pipe cleaner up the gas tube are there any other gas ports/holes that should/can be cleaned? Obviously there must be holes in the barrel to bleed off the gasses, but can those be clogged/cleaned?

 

[problemchild]

Re: AR not running

What position of the clock is the brass landing? (1, 2, 3 etc)?
Is brass all in one nice pile?
Any claw marks on the rim of brass?
Have you checked the rings to make sure they are not all gap aligned in the same spot?
Did the rings get rusty and damaged while it sat for 2 months? (this happened to me).
Same exact ammo as last time or just same brand?
Same exact magazine as last or just same brand?

 

[country888]

Re: AR not running

Check the gas key & gas block! Make sure their tight & haven't moved.

 

[ToddM]

Re: AR not running

Think I might have found it, I pulled the forearm off and the two lower gas block set screws were both loose, the forward one a full turn and the rear a half turn. I didn't pull the forearm the last couple cleaning sessions and check the gas block bolts.

Can they be red lock tighted, or staked?

Brass landing at 2-3
gas rings I checked both times cleaning
same batch of ammo and mags

 

[redirt78]

Re: AR not running

There is the also the gas port that goes from the barrel into the gas block then through the gas tube. Since the gas block was loose you might as well pull it off and look for buildup.

 

[bustin]

Re: AR not running

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ToddM</div><div class="ubbcode-body">Think I might have found it, I pulled the forearm off and the two lower gas block set screws were both loose, the forward one a full turn and the rear a half turn. I didn't pull the forearm the last couple cleaning sessions and check the gas block bolts.

Can they be red lock tighted, or staked?

Brass landing at 2-3
gas rings I checked both times cleaning
same batch of ammo and mags </div></div>
A couple of things, remove the Gb, rub a little blue locktite on the barrel under the GB.
replace and tighten. When you get to the range and warm up the barrel tighten the set screws again. when it cools off they will not come loose but you will need to warm the barrel again before you can loosen them. Torch works too.
GBs are thin, when warmed up they will grow and the screws will loosen.

 

[txdrhuntr]

Re: AR not running

I had a similar problem with my AR. Tried most everything suggested here without solving the problem. Even bought and installed a new gas block. Well, I had not thought of the KISS solution first, finally checked by gas rings and found out I had worn them out. Replaced the gas rings and it runs like a sewing machine! When I stood the carrier with bolt installed on the bolt, the carrier slid down right away. Once the new rings were installed and I checked again, the carrier doesn't slide down the bolt. Could have saved a few bucks if I'd thougth to check the obvious first.

 

[mtrmn]

Re: AR not running

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ToddM</div><div class="ubbcode-body">Think I might have found it, I pulled the forearm off and the two lower gas block set screws were both loose, the forward one a full turn and the rear a half turn. I didn't pull the forearm the last couple cleaning sessions and check the gas block bolts.

Can they be red lock tighted, or staked?

Brass landing at 2-3
gas rings I checked both times cleaning
same batch of ammo and mags </div></div>

I wouldn't use red or stake--you may have to undo that one day. Use blue loctite on the set screws, it's good enough to keep them from backing out. If it's loose, the gas hole may be partially blocked due to slight misalignment.

 

[USACS]

Re: AR not running

If you're having problems, you can either have it worked on through the warranty, or do the work yourself. S&W has among the best warranties and customer service in the gun industry. They will fix your problem or die trying. If you contact them, ask them if they can pin the gas block if you send it in. A taper pin is far more secure and reliable than set-screws.

If you want to do the work yourself and don't want to make a warranty claim, you need to make sure the gas block is secure and that you have a solid seal. Attempt to remove it and see if there is any play. The gas block should be very snug and you should either have to twist of back and forth while pulling back, or need to tap it with a mallet to move it back. If there is no play, there is no reason to be putting loctite on the barrel around the gas port. If there is play or a gap, putting loctite on it is putting a bandaid on a bullet wound. If that's the case, get a new gas block. If there is no play, then your gas block is fine. Get the gas block pinned with a taper pin.

Loctite can eventually fail due to the heat. I've seen Rocksett treated screws back out. Staking the screws after torquing them down will work, but if you ever have to back them out, you will trash the gas block and need a new one. The same goes for the screws, as you would do well to counter-stake them as well. Pinning is the most sure-fire method of making sure that block is secure.

Also, make sure that your gas key is secure, the screws are properly staked, inspect the bolt gas rings for damage or unusual wear, inspect the bolt for any damage, and then inspect the inside of the carrier to ensure there is chrome in there. S&W sold a batch of M&P15s a while back that didn't have chrome in the carrier. Most were recalled and replaced, but you won't know if you have this issue or not until you check. The best way to do an overall check of the bolt is to pull bolt all the way forward in the carrier (while it's assembled), and then stand it up the bolt face on a flat surface and see if it holds, or if it collapses. You can tap or hit the table to coax it forward to gauge how much resistance there is. If there is very little resistance, you probably have bad gas rings, or else a worn/damaged bolt.

Also, check your gas tube for a good seal. There should be a good bell around the end where it interfaces into the gas key. Feel for flat spots on the bell that indicates wearing on the inside of the key. If there is any flat spotting, jiggle the gas tube back and forth. There should be play in the gas tube as it goes through the upper receiver opening. Sometimes a barrel nut is improperly indexed, and can push the gas tube over to one side (DPMS is notorious for this), causing it to wear on the inside of the gas key. If this is detected, properly adjust the barrel nut and then replace the gas tube.

 

[ToddM]

Re: AR not running

Good info, and thanks to everyone that has helped out in this.

The gas block is not what I'd call "sloppy" but it certainly would not need hard twisting or tapping to get it on/off, but it doesn't feel like it has any play either. So perhaps it's not as snug as it could/should be.

Bolt passes the gas ring check with no problem, gas tube seems fine. I'll have to check on the chrome lined carrier, never thought to look or heard about the recall issue to bother looking.

Funny part is I can remember a few months ago when I was shooting it more often I tried out a buddies hydro buffer and decided against it because seemed to cause it to short stroke on rare occasions. Well I bet it wasn't the hydro buffer it was this gas block loosening up.

 

[Andy T]

Re: AR not running

Are you running the rifle well lubricated?

 

[cz777]

Re: AR not running

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: country888</div><div class="ubbcode-body">Check the gas key & gas block! Make sure their tight & haven't moved.</div></div> look around the gas key for black scoot -if not use some white paint at base and test fire ...next is the gas rings broken ??? front sight block loose ? gas tube clear ?

 

[ToddM]

Re: AR not running

I ran it lubed but not "wet" normally in the past. When I noticed I had issues, the next two times I cleaned it and really lubed it well and it didn't help.

I'll get it out to the range next week but I think those loose gas block screws are going to be the culprit. I didn't see any obvious gas leaks in the bolt/key area, but the inside of the hardguard and barrel by the gas block was ugly.

Gas rings seemed fine, but I ordered some spares just for giggles.

Getting my butt kicked by guns this week, I had to fit a new extractor to my little browning buckmark I just got as well. It must have been 4:59 pm on Friday when they fit the stock one it was ugly.

 

[10ringping]

Re: AR not running

If that's not it you might need a heavier buffer.

 

[ToddM]

Re: AR not running

Got it out to the range today, no joy.

Still short stroking, it ejects fine but still won't hold the bolt back on a mag, if anything it's worse now after tightening the gas block, and that's still running with a cut down recoil spring and standard carbine buffer.

I'm going to pull it down tonight and mark the gas block/barrel before I remove it and see if I didn't get it centered when I tightened it up. I tried to align it so there was no torque/twist on the gas tube at the upper, but perhaps that it was bent/damaged when it was loose before. I also snugged it up against the collar, perhaps that was too far.

Is there any way to ensure the gas block hole is aligned with the hole in the barrel while it's installed?

Outside of that I'm at a loss now, the gas rings seem fine, there's tension on the bolt, I don't see any other obvious signs of leaking, so if it seems lined up I'm probably just going to have it sent into S&W and let them figure it out. It's just annoying because it used to run like a guy with a TV on his shoulder in a riot.

 

[RugerSlinger]

Re: AR not running

Check the buffer tube for any obstructions, do you lube your buffer spring?(I know its a big no no) Maybe its dirty in there and causing extra friction. If its not that then it is definitely in the gas system, clogged tube or gas block not properly aligned.

 

[Bedlam]

Re: AR not running

I've had these symptoms on two different guns.

The first time it was the gas key coming loose from the bolt carrier. Tightened the bolts and restaked. Works perfect now.

The second time it was fixed by removing the o-ring from under the extractor. I was pretty annoyed to find that o-ring under there since I did not ask for it. Apparently Noveske just includes them on their bolts whether you want them or not. I don't know if S&W includes them or not, but you might as well check. Anyway, I removed the o-ring and it works perfectly now.

 

[ToddM]

Re: AR not running

I'll check the gas key bolts, I know I checked when I first got it that they were staked but haven't actually checked to see if they are loose, or have loosened.

I also haven't checked for an O-ring under the extractor but I will and if it's there I'll try it without. I know I've read about that before was it supposed to improve extraction/ejection?

 

[Bedlam]

Re: AR not running

Yes the o-ring is supposed to improve extraction. But I wouldn't add one by default, I'd only add one if there are extraction problems. In my case it actually caused problems.

 

[redirt78]

Re: AR not running

Sucks to hear you're still having problems. I have learned a thing or two from your thread though. I guess once you get it right you can look at the bright side, by that time you'll know your gun inside and out. Good luck man hope you get it soon.

 

[ToddM]

Re: AR not running

Pulled it down again, gas key bolts they were staked and solid. It did have an O-ring under the extractor so I removed it. I also replaced the gas rings even though the new ones don't seem to be any different the bolt did and still does easily pass the "stand up" test.

I marked the gas block and barrel so when I removed it I could try to verify that they were lined up and they were. I checked not only that the holes were centered in circumference but also that if the block was snug up against the shoulder of the barrel that the block would not be too far forward/backward to line up, all good.

One thing I did notice is on the end of the gas tube that goes into the carrier one side of the mushroom "bulb" oversize end of the gas tube is worn down flush with the normal tube wall. I'll order a new gas tube, but from reading other posts it doesn't seem like this should be enough of an issue to cause this big of a problem, especially since the MP15's are considered over-gassed as is, but maybe. It also looks like it might be leaking a bit where the gas tube goes into the gas block itself.

I'll order a new gas tube see if that helps, I'll probably try another low pro gas block as well since this one seems a little more loose than would be ideal from the sound of it.

Man what is it with AR parts right now, nothing is available!

 

[Bedlam]

Re: AR not running

Is it working now or still waiting for parts?

 

[Blackrifle1]

Re: AR not running

I would take it to the dealer that sold the rifle to you and have them solve the problem - S&w or their authorized dealer should take care of this for you. good luck!

 

[ToddM]

Re: AR not running

Heh, well it's kind of sorted and may be as sorted as it's going to get.

I replaced the gas tube, gas block, gas key block, did another full down cleaning, replaced the recoil spring and verified the buffer weight as being correct for a carbine. Put all the factory parts back on and retested it.

It now runs 100% with winchester white box, federal, hornady ammo, but it still won't run wolf black box without short stroking. Throws the brass at about 4 o'clock, and even runs fine with a heavier buffer.

Now looking around the internet there's all sorts of posts about wolf black box not running because it's too soft/weak, but when the gun was new it ran it no problem.

However I'm wondering if I got a bad batch because it chewed it up no problem before, but I did noticed the stuff I was having problems with at the range the other day was really soft shooting compared to all the other ammo that ran okay. I've mixed in wolf black box in the past with other ammo and never noticed this much difference even other guys at the range said right away they noticed there was a huge difference in sound with the black box and shooting it was totally obvious.

So right now to summarize I think the loose gas block, and gas tube being wore fixed the gun side of the issue, and now it's just that I've got some really weak wolf black box to shoot up.

 

[EagleScout501]

Re: AR not running

you might find, by putting the old recoil spring back on, that it might run fine with wolf black box.

 

[ToddM]

Re: AR not running

Yeah, I tried that at the range, even with an old recoil spring with about 1.5" cut off it and a stock carbine buffer it wouldn't run. It would fire and eject, but the cases barely made it out of the ejection port, maybe went a foot or two, everything else was going 8-10' easy with that setup, and a solid 6-8' with a tubbs spring and ST-T2 buffer.

Like I said it's really weak ammo, I have a new case of mil classic wolf and another case of black box I haven't opened so I'm going to try a couple boxes out of each of those cases out see if it has more oomph to it, because I've ran a lot of wolf through that gun in the past without major problems. I know in the past at the range I've ran mixed ammo as well and noticed a tiny difference between brands, but nothing like this.

I really think I just got a bad few boxes because this stuff is super soft. So I'm hoping it's just the few loose boxes I have around and the other two cases will run fine.

 

[EagleScout501]

Re: AR not running

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ToddM</div><div class="ubbcode-body">Yeah, I tried that at the range, even with an old recoil spring with about 1.5" cut off it and a stock carbine buffer it wouldn't run. It would fire and eject, but the cases barely made it out of the ejection port, maybe went a foot or two, everything else was going 8-10' easy with that setup, and a solid 6-8' with a tubbs spring and ST-T2 buffer.

Like I said it's really weak ammo, I have a new case of mil classic wolf and another case of black box I haven't opened so I'm going to try a couple boxes out of each of those cases out see if it has more oomph to it, because I've ran a lot of wolf through that gun in the past without major problems. I know in the past at the range I've ran mixed ammo as well and noticed a tiny difference between brands, but nothing like this.

I really think I just got a bad few boxes because this stuff is super soft. So I'm hoping it's just the few loose boxes I have around and the other two cases will run fine. </div></div>

i had a problem like this with a gun i built once before from parts, the 1st mag it started doing this. This is also why I bring at least 3 different types of ammo with me every time i try a new gun. The wolf did to me exactly what it is doing to you. So i grabbed a bag of 200 XM193's out of the truck and after that 200 the gun ate the wolf just fine. Your situation is quite unique though.