View Full Version : Previously reliable AR suddenly not cycling.
So I went to the range this morning and my AR, which has been 100% reliable to date, abruptly quit cycling.
I fired a few shots and then had one round get hung up half-fed into the chamber. Resumed shooting, another couple rounds and the bolt failed to lock open on the last round. Changed mags, chambered the first round and fired, ejection pattern seemed different and bolt failed to pick up the next round, skidding over the top of it instead, leaving a scrape on the brass.
This pattern of chambering the first round, firing, different ejection pattern, and the bolt riding over the next round in the mag and not feeding continued until I gave up. Four different mags and two types of ammo were used all with the same results.
The gun seemed to be short-cycling. I took it apart and noticed nothing amiss, as best I can tell the gas key is unobstructed.
Rifle: BCM midlength upper on a lower with a rifle buffer and spring. Gun has been 100% until today when it has a complete meltdown.
Ammo: Privi M193 and Radway Green SS109, gun has had no issues with either type, and several others, including Wolf, in the past.
Magazines: two Magpul 20-rounders, a Magpul 10-rounder, and an Okay GI 30. None of these mags have ever had issues in this gun or in any others.
Lube: Slip EWL30. My usual lubricant. Gun was amply lubricated.
Ejection: normally this gun ejects at around 4 O'clock or so, I did notice that it seemed to be throwing them out at closer to 3 O'clock and not quite as far as usual. I didn't examine the brass as it landed in the snow but in hindsight I wish I'd dug some of it up.
Environmental factors: approximately 30 degrees. I add this because I'm wondering if perhaps the thicker Slip EWL may have been gumming up the gun somehow in the cold weather. EWL is my regular lube but this is my first time shooting this gun in weather this cold. Although a week ago I shot the gun in only slightly warmer 33 degree weather, with the same ammo and mags, without issue.
Any ideas?
I had a rifle do this. The gas key was loose.
Sounds like it's maybe short stroking. Does the BCG move freely and smoothly when you hand cycle it? If the gas key isn't loose are your gas rings in good order? Does the gas tube look good or is the raised part on the outlet wore off?
I checked the gas key, it's a BCM and is staked well, and it *seemed* alright in my initial examination but perhaps I need to look at it more closely.
Sounds like it's maybe short stroking. Does the BCG move freely and smoothly when you hand cycle it? If the gas key isn't loose are your gas rings in good order? Does the gas tube look good or is the raised part on the outlet wore off?
Yeah everything seems alright. The gas rings were changed out maybe a couple hundred rounds ago and seem alright. Gas tube looks fine too as far as I can tell but I might have to go back over the gun's components with a fine toothed comb. It's just odd to me that it went from previously perfect to total dumpster fire.
Is the upper fully stock and unmodified? Could the gas block have gotten loose?
Is the upper fully stock and unmodified? Could the gas block have gotten loose?
The only alterations I've made to the upper are things like the handguards and the flash hider, I haven't touched the gas system at all. The FSB doesn't seem to be loose
Double checked the gas key screws, they seem fine.
Took a bunch of pics. Does it look like I might have a gas leak somewhere?
http://i.imgur.com/px1z6Kp.jpg
http://i.imgur.com/nc3dnV5.jpg
http://i.imgur.com/GJMOoZt.jpg
http://i.imgur.com/qorKaiO.jpg
http://i.imgur.com/5cWnTvr.jpg
http://i.imgur.com/GqPO5ZE.jpg
http://i.imgur.com/o0KcBUk.jpg
Gas tube wear? It is hard to say from the last picture, but it looks like the mushroom at the end could have worn down a bit. That could be a cause for the symptoms you are experiencing. Slightly misaligned gas tube is often missed in regular cleaning and inspection, and it causes accelerated wear to the gas tube mushroom.
Maybe it's just me, but I see no roll pin in your FSB. If the roll pin somehow fell out, your gas tube might have moved back a tad causing insufficient gas to cycle.
There is a roll pin present, it just doesn't show up well in the pics.
Gas tube wear? It is hard to say from the last picture, but it looks like the mushroom at the end could have worn down a bit. That could be a cause for the symptoms you are experiencing. Slightly misaligned gas tube is often missed in regular cleaning and inspection, and it causes accelerated wear to the gas tube mushroom.
It doesn't appear particularly worn when compared to a couple spare BCM tubes I have on hand, a new one and one that had seen light use. Unfortunately those two are both carbine-length ones.
My best best seems like it might be to preemptively order a new gas tube and replace the one in the gun and clean the BCG etc off and perhaps try the thinner Slip 2000 vs the thicker EWL30.
This has been a really good gun up until this morning and I'd like to get back up and running again ASAP.
Maybe it's just me, but I see no roll pin in your FSB. If the roll pin somehow fell out, your gas tube might have moved back a tad causing insufficient gas to cycle.
Yeah, it does look to be missing. If you don't have a gas tube roll pin, you'll want one.
There is a roll pin present, it just doesn't show up well in the pics.
Gotcha
I suppose I could also try sticking the bolt into another carrier and see if the gun will run like that.
Swap in a known good carrier.
Take the buffer and spring out, check the roll pin in the buffer and see if it's walking out and dragging on the spring.
There is a roll pin present, it just doesn't show up well in the pics.
It doesn't appear particularly worn when compared to a couple spare BCM tubes I have on hand, a new one and one that had seen light use. Unfortunately those two are both carbine-length ones.
My best best seems like it might be to preemptively order a new gas tube and replace the one in the gun and clean the BCG etc off and perhaps try the thinner Slip 2000 vs the thicker EWL30.
This has been a really good gun up until this morning and I'd like to get back up and running again ASAP.
The end of the gas tube looks fine, and your oil isn't the problem. After checking the spring and buffer like ST1911 said, with the gun all back together, retract the bolt back and forth. Are you feeling any unusual mechanical interference?
Also you said you C/O the rings 200 rounds ago. I have had guns short stroke temporarily until I got them broke in. This hasn't happen every time, but it did happen.
Roll pin in the buffer isn't protruding and doesn't seem to be loose.
No interference that I can detect while hand-cycling the bolt. I can ride the charging handle and slowly ease the bolt home and it will still go into battery without issue.
I did brace myself for potential cycling issues right after changing the gas rings out, but it functioned fine. It seems odd that now after at least a couple hundred rounds that they would suddenly cause the gun to choke. Again it's not like I've been having intermittent short stroking that's been getting progressively worse. I went from 100% function to having to hand cycle every cartridge into the chamber within a matter of a few rounds.
I'm wondering if there's some obstruction in the gas key/carrier that I'm not seeing, however I was able to feed a twist-tie (I didn't have any pipe cleaners on hand) from the gas key down into the carrier, it's pretty flexible so anything offering resistance in there probably would have stopped it.
Could there be some sort of obstruction in the gas tube itself?
Swap in a known good carrier.
This is the most logical place to start. Until the BCG is eliminated as the source of trouble, anything else is a waste of time.
How many rounds do you have on the gun total? And when you said rifle length buffer and tube, did you mean A5?
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Roll pin in the buffer isn't protruding and doesn't seem to be loose.
No interference that I can detect while hand-cycling the bolt. I can ride the charging handle and slowly ease the bolt home and it will still go into battery without issue.
I did brace myself for potential cycling issues right after changing the gas rings out, but it functioned fine. It seems odd that now after at least a couple hundred rounds that they would suddenly cause the gun to choke. Again it's not like I've been having intermittent short stroking that's been getting progressively worse. I went from 100% function to having to hand cycle every cartridge into the chamber within a matter of a few rounds.
I'm wondering if there's some obstruction in the gas key/carrier that I'm not seeing, however I was able to feed a twist-tie (I didn't have any pipe cleaners on hand) from the gas key down into the carrier, it's pretty flexible so anything offering resistance in there probably would have stopped it.
Could there be some sort of obstruction in the gas tube itself?
While you're looking for a spare BCG, you could see if there is an obstruction in the gas key. There have been cases of popped primers winding up in the gas key.
Gas tube wear? It is hard to say from the last picture, but it looks like the mushroom at the end could have worn down a bit. That could be a cause for the symptoms you are experiencing. Slightly misaligned gas tube is often missed in regular cleaning and inspection, and it causes accelerated wear to the gas tube mushroom.
I had this happen....previously reliable rifle suddenly not cycling. Ultimately, after reinstalling the gas block and trying a different BCG, I changed out the gas tube even though it looked OK. That fixed it.
I don't know how many rounds the OP has on his gun, but after looking at the pictures of his gas tube, do you think it's worn out? Honest question. It looked ok to me.
A couple thousand probably. Most of that in the last three months.
I'm not using an A5, it has a standard rifle receiver extension and a standard rifle buffer, 16" barrel, mid length gas system.
This is the most logical place to start. Until the BCG is eliminated as the source of trouble, anything else is a waste of time.
Intellectually, I know this is correct, however it could be as long as another week before I can get to the range again (it gets dark at like 4pm currently) so I feel compelled to pick over the gun piece by piece in the meantime.
While you're looking for a spare BCG, you could see if there is an obstruction in the gas key. There have been cases of popped primers winding up in the gas key.
Seems like there isn't anything in there but I'll have to try it again with an actual pipe cleaner instead of the twist tie I tried.
Luckily I have a spare carrier that I can drop in, it's seen some use (200-300 rounds or so) so I know it works.
I agree with Mistwolf. Run a different BCG and see it the problem is cured. If so, then investigate the BCG. I assume you have completely disassembled the BCG and the bolt and checked it for issues? Let me preface my next comment; I just got new glasses and it is hell for a week trying to get use to new glasses for me. If I am seeing the picture correctly of the gas tube as it enters the upper receiver, it looks like there may be a gas leak. I could very well be seeing it incorrectly or misinterpreting the picture. It appears to look like a bit of blow-by, but I may be misinterpreting the picture.
Cheers, Steve
I don't know how many rounds the OP has on his gun, but after looking at the pictures of his gas tube, do you think it's worn out? Honest question. It looked ok to me.
Mine looked OK too. Swapping it out fixed the problem.
Mine looked OK too. Swapping it out fixed the problem.
Gotcha. If nothing else comes to light, it would be something to try. I'll be keeping this for future use... "don't be fooled by appearances".
I agree with Mistwolf. Run a different BCG and see it the problem is cured. If so, then investigate the BCG. I assume you have completely disassembled the BCG and the bolt and checked it for issues? Let me preface my next comment; I just got new glasses and it is hell for a week trying to get use to new glasses for me. If I am seeing the picture correctly of the gas tube as it enters the upper receiver, it looks like there may be a gas leak. I could very well be seeing it incorrectly or misinterpreting the picture. It appears to look like a bit of blow-by, but I may be misinterpreting the picture.
Cheers, Steve
Yes, BCG was taken apart and examined, nothing jumped out at me as seeming awry, but I'm no armorer. I thought the area around where the gas tube enters the receiver looked somewhat strangely gunked up as well, which is why I included a pic of that spot. I'm wondering if the tube could have ruptured or something just inside the receiver, but I think I'm going to try a bolt carrier swap before I go yanking the tube out because it could also be just excess grease and crap that's gotten in there and gotten cooked by the gas tube.
I don't know how many rounds the OP has on his gun, but after looking at the pictures of his gas tube, do you think it's worn out? Honest question. It looked ok to me.
I don’t remember the exact specs for the gas tube, but I think the mushroom for a new tube should measure approximately .180 and problems will start at around .170 or thereabouts. Visual inspection is going to be difficult. The tube can also erode at the gas port, which is not easy to diagnose without removing it.
Glock9mm1990
12-11-17, 03:00
I agree with what others have suggested try a different BCG and see if that fixes the problem. If however that doesn’t fix it I would email BCM if I were you and send the upper back because there is no reason a BCM upper should stop working after only a few thousand rounds, I believe they do come with a lifetime warranty to the original owner. Let us know what the problem turns out to be and what the fix is.
I don’t remember the exact specs for the gas tube, but I think the mushroom for a new tube should measure approximately .180 and problems will start at around .170 or thereabouts. Visual inspection is going to be difficult. The tube can also erode at the gas port, which is not easy to diagnose without removing it.
Thanks for the info.
The culprit would seem to be the bolt carrier itself.
Took the gun back to the range after work today, racing against the clock since my local range doesn't allow shooting after sunset, which currently comes at about 4pm.
Just to double check, I first fired the gun with the same carrier. Identical results to yesterday. Weak ejection and total failure to feed rounds out of the magazine.
Took the bolt, firing pin, firing pin retaining pin and cam pin out and put them in a second BCM carrier. Gun functioned normally, locked open on the last round, healthy ejection. Fired about 35 rounds and had to pack up due to sunset.
So I must either have a gas key that's loose after all or that has some kind of obstruction in it that I haven't yet detected.
Using a Wheeler Fat Wrench on the gas key screws revealed that the front one was in fact loose. So I'm assuming this is the source of the short-stroking.
The rear screw is properly torqued to at least 50 inch pounds.
So is this a "send it back to BCM for repairs" thing or a fix it myself thing?
Contact BCM. Work with them to resolve the issue to your satisfaction. My 2 cents.
I am glad you isolated the problem!
Andy
Me too, the screw was not overly loose, but it was just enough I guess. Doesnt take much apparently. After ruling out the gas tube as the source of the problem at the range earlier I decided to really take a hard look at the gas key. The loose screw was torqued to less than 35 inch-pounds by time I noticed it. It would seem the staking was insufficient. I'll get in touch with BCM and go from there. If it turns out I have to fix it myself it's not a big deal. The carrier is actually one I bought in 2009, aside from a carbine class in 2013 the rifle it was in didn't see much use until this fall when I really started shooting it regularly.
Test the BC after you tighten the bolt before you declare victory...
Glock9mm1990
12-11-17, 19:38
Let us know how BCM responds.
Test the BC after you tighten the bolt before you declare victory...
I will definitely be testing it before trusting it in another gun. At least it's a fixable problem. For now, I've got the other carrier in my rifle.
Had the same issue with a C4 carrier, torqueing the key fasteners to spec and re-striking the stake corrected the issue and it's run great since even with sloppy loose rings. This BCG was sent back to mfg in the malfunctioning upper and returned loose.
Part of the reason my range spares kit includes a full BCG along with various buffers.
Very easy to rule this out on the spot instead of getting frustrated waiting to go back to the range.
Glad you got your stick back in the fight!
BCM has sent me a return form so they can replace the BCG, which is good of them. I'd have been happy just sending it in and getting the gas key re-torqued and re-staked.
BCM has sent me a return form so they can replace the BCG, which is good of them. I'd have been happy just sending it in and getting the gas key re-torqued and re-staked.
From your description of several thousand rounds on the BCG and apparently several years, I think that is pretty stand up of them.
As you said, I would have expected them to have you send it in.
I have to admit, the several stories like this I've recently read are swaying me to start paying a little more for this kind of 'insurance' from BCM.
The screw possibly sheared and that's why it is moving, or it just wasn't staked right. My bet is on the sheared screw.
Using a Wheeler Fat Wrench on the gas key screws revealed that the front one was in fact loose. So I'm assuming this is the source of the short-stroking.
The rear screw is properly torqued to at least 50 inch pounds.
So is this a "send it back to BCM for repairs" thing or a fix it myself thing?
The screw possibly sheared and that's why it is moving, or it just wasn't staked right. My bet is on the sheared screw.
I didn't remove the screw completely so I don't know for sure, but-
again total amateur-hour speculation on my part here- but that does sound possibly more consistent with the sudden, complete loss of function vs a more gradual loss of reliable function that I'd think would accompany the screw loosening over time.
I could have avoided a lot of speculation if I had just paid closer attention to those gas key screws upon my initial examination after Sunday's ill fated range trip, but I wanted to rule out the gas tube as the cause before I started really dicking with the bolt carrier and potentially causing myself more problems.
This is a good case study of why it is good not just to have spare bolts, but to have at least one spare carrier, as well.
Yeah, if I hadn't had an unused carrier kicking around I could still have pirated one from another rifle just for the function test but having a spare will allow me to keep the midlength in a functional state.
Actually bringing some spare parts *with* me to the range might be a good idea going forward though.
Any blown primers before this event? I once had this problem and finally traced it back to hot ammo that blew primers and a primer anvil got stuck in gas key. Never found it until I removed gas key.
Edit. Looks like you solved it....
Upon further inspection, Iraqgunz was indeed right on the money about the screw being sheared.
wetidlerjr
12-16-17, 17:46
Upon further inspection, Iraqgunz was indeed right on the money about the screw being sheared.
Hmmm.... Imagine that. :smile:
https://vimeo.com/150181996
Upon further inspection, Iraqgunz was indeed right on the money about the screw being sheared.
https://vimeo.com/150181996
Upon further inspection, Iraqgunz was indeed right on the money about the screw being sheared.
https://vimeo.com/150181996
Aaannndddd that's why I joined this forum.
Great thread.
Enjoyed reading it and as the OP says, very helpful members here.
sundance435
12-29-17, 08:02
Upon further inspection, Iraqgunz was indeed right on the money about the screw being sheared.
He's a credit to the board and one of the reasons I come here first for info - also puts out a damn fine carbine. On another note, you guys have convinced me to add a full BCG to my range bag, not just a bolt.
The screw possibly sheared and that's why it is moving, or it just wasn't staked right. My bet is on the sheared screw.
Gunz, for us un-educated folks, what would cause the screw to be sheared-off?
Stress corrosion cracking? Heat, gases. Not sure in nitrogen embrittlement could be a factor—i’m Throwing guesses & hoping I’gunz might be impressed by a neophyte like me:rolleyes:
I had a rifle do this. The gas key was loose.
That would be the first place to look.
If it appears to you that the gas key is fine, you can check by putting a different carrier in that rifle and see if you get the same results. If the results are the same you can at least eliminate that from the mix.
Upon finding that the screw was sheared in half, as Iraqgunz had indicated, I just chalked it up to "shit happens". BCM took care of it and sent me an entirely new BCG. It's in the gun now but various forms of uncooperative winter weather has kept me from getting back to the range thus far.
:rolleyes:There’s normal wear & tear, true, but the nerd in me always wants to know “why?” Why the one & not the other? Was on3 of the screws torques too tight or too loose? Was the screw alloy off? Was heat treatment off?
I admit we never know all the variables & “shit happens” winds up as the diagnosis. I’d have probably replaced both screws, torqued & staked....but my OCD meds may be off....:rolleyes:
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