My AR stopped working?

[Viperdoc]

Was in the midst of shooting a ladder yesterday when my AR becamea single shot. Nothing had obviously changed, and I shot at least 50 rounds prior.

However, the day before I did remove the gas block and tube, and did re torque the barrel. I checked the gas tube tonight and it was aligned with the bolt carrier with no binding.

Any other ideas?

 

[itchyTF]

Did the gas block slide away from the gas port by any chance? Is the tube obstructed with something?

 

[Viperdoc]

Will check, but gas block alignment looked good. Need to remove handguard. Any other ideas?

 

[kentuckytroutbum]

Did the gas block slide away from the gas port by any chance? Is the tube obstructed with something?

Besides what itchy said, check the key on top of the bolt carrier to see if it is obstructed. Also, check for carbon build up in the rear part of the carrier. Did you ding the gas tube at the star barrel nut?

Also, check your gas rings on the rear of the bolt. Are they cracked?. Are the slots in the rings aligned? If they are, the slots needs to be offset from each other, or you will get gas blow by, and it will short cycle.

Check the cam pin, and also check to be sure that the bolt is rotating freely in the carrier, with & without the cam pin.

Check your recoil spring in the extension tube. It may be binding, or kinked, and may need to be replaced.

Let us know if you have solved the problem.

Bill

 

[7stubby]

Is it dry? I once had a AR that wasn't lube properly and would shoot one then wouldn't cycle. Lubed it up and back at it again. ;D Just my 2 cents.

 

[Minesweeper3433]

Good way to figure out some of the problems that ARs get is have a freind stand/sit to your 3 oclock while shooting and they can watch the weapon cycle. If it is short strokeing then it is getting gas just not enough for some reason or it has an abnormal amount of friction.

 

[rcw3]

There is not enough information provided for anyone to make a proper analysis of this situation (it's all just guessing at this point).

My first question would be what do you mean when you say the rifle "became a single shot"? Does that mean no cycling, partial cycling, or just not cycling back far enough to pick up the next round out of the magazine but far enough to eject the spent case?

In the back of my mind I am questioning why it was felt that the barrel needed to be re-torqued, and exactly how that was done, what tools used, what was secured and what was torqued (that may give definite clues as to what may have happened here).

What kind of gas block is it, slip on (with underneath set screw), clamp on, pin on, adjustable gas block, or some other set up?

Robert

 

[Viperdoc]

The rifle does this: Gun fires, bolt moves a little, maybe less than half an inch but not enough to cock hammer, brass does not eject. Super short stroke.

Gas block is a Krieger, fixed with set screw using blue locktight. Gas tube slides into key easily, no binding. First sixty or so rounds fired easily and normally. Then, gun became a single shot.

I did not dissemble BCG to look at gas rings, but a great idea.

My uneducated guess is that gun suddenly stopped getting enough gas after working fine.

I have a heavy barrel match/varmint with a free float hand guard and heavy scope, and noticed some slight motion of the hand guard when picking up rifle. First thought it was the hand guard lock nut, but turned out the barrel nut was a little loose, but of course limited by the gas tube. So, I removed hand guard, gas block and tube, then torqued the barrel nut ( one more hole or 50-60lbs).

Reassembled all, and was working up a reload ladder when gun FTF by super short stroking. Considering gun worked fine for 60 rounds, do not think it was my disassembly that was the culprit, but have certainly screwed up before, so am looking for advice.

 

[5spd]

I would strip the BCG and clean it all up and check the key to see ifs its catching while in motion, lube it up good and try it again. SS is usually gas/BCG, underpowered ammo/ junk in the upper.

 

[Matt Pitchon]

In addition to the other comments. I recently had the roll pin fall out of the gas block. The roll pin holds the gas tube in place. If the roll pin is missing, the gas comes out of the roll pin hole, and the gun won't cycle. I have a Kreiger barrel and gas block. When the pin fell out, it would short stroke.

 

[rcw3]

First thing to do is see if you can isolate the source of the problem before you just start guessing what it is and doing things without feedback on the problem.

I still feel something may be related to the work done on the rifle (even though you said there were about 50 or so rounds fired after the work was done).

Seems to me the problem is either a gas issue or a mechanical issue. Here's where I would go with that:

1. See if with the charging handle, and no ammo in the gun and without a magazine, you can cycle the gun a few times by hand, pulling the carrier all the way back and when you let it forward it goes into lock up with no apparent issues. If it seems to do that without any particular issues or difficulty, then try it with an empty magazine in the gun (using the bolt release to let it go). If nothing seems awry, then move on. If there's difficulty doing that, then chances are there's a mechanical issue.

2. Remove the upper from your lower and stick you finger in the back end of the bolt carrier and see of you can relatively easily cycle the carrier in and out to see if the bolt goes in and out of lock up relatively easily. If there are issues doing that, further investigation (and action) may be in order, but if the carrier goes in and out of lockup without any weird clunking or noises (i.e. beyond what an AR-15 normally sounds like going in and out of lockup) and without needing excess force to do that, then chances are it's something else.

3. While the upper is off, something quick and easy to check (for a mechanical issue that affects the gas system) is to see if the gas key on the carrier is tight (i.e just check the screws that hold it on the carrier with an allen wrench and make sure neither screw is loose or broken - don't typically need to do anything special or crank them down hard, etc. - just make sure they are there and not loose or broken).

4. If nothing seems awry so far I would then tend to verify that the gas port in the barrel is lined up with the hole in the gas block and that the block is secure to the barrel. After the prior re-torquing of the barrel nut, I would not assume the port in the barrel sits top dead center. The barrel and barrel extension could have rotated some in the upper receiver (tweaking barrel extension locating pin and the channel it sits in) when the barrel nut was torqued up and that can cause alignment issues.

So check things out and see where we go from there. In the course of 1-4 above, something may become apparent that indicates what's going on. Please feel free to post additional findings and questions and go from there.

Good luck!

Robert

 

[Viperdoc]

Think I found the problem. On close inspection, the gas block had moved up the barrel away from the barrel step around 2mm. The set screw was tight. I tapped the gas block back into position and re tightened the set screw at least two fingers tight, until I got some flex in the Allen key, with some locktight.

The bcg slid in and out of the upper easily, with no apparent contact between the gas tube and the key. The key was tight and staked in place.

I suspect the recoil made the gas block slide up the barrel. I did notice some mild pitting and corrosion under the gas block (gas residue and perhaps dissimilar metal corrosion?), so I did put some minimal anti seize under the block, with the hopes that it would not corrode into place and would be easily removable. Probably lubing under the block was not a great idea.

Thanks for all the great advice!(of course I haven't actually fired it yet, but am pretty confident this was the problem).

 

[AdamJ]

Make a witness mark through the gas block set screw hole, remove gas block and make a dimple in the barrel with a small drill bit. Just enough to give the set screw a place to "lock in at", don't go over board with the dimple depth. I have used a 1/8" bit and it is just right to get a little dimple that the set screw can lock in to. Good luck, this is the reason I don't like any gas block but a taper pinned one.

 

[rcw3]

Think I found the problem. On close inspection, the gas block had moved up the barrel away from the barrel step around 2mm. The set screw was tight. I tapped the gas block back into position and re tightened the set screw at least two fingers tight, until I got some flex in the Allen key, with some locktight.

The bcg slid in and out of the upper easily, with no apparent contact between the gas tube and the key. The key was tight and staked in place.

I suspect the recoil made the gas block slide up the barrel. I did notice some mild pitting and corrosion under the gas block (gas residue and perhaps dissimilar metal corrosion?), so I did put some minimal anti seize under the block, with the hopes that it would not corrode into place and would be easily removable. Probably lubing under the block was not a great idea.

Thanks for all the great advice!(of course I haven't actually fired it yet, but am pretty confident this was the problem).

Great news! Sounds like you found the issue. That's why I dislike those slip on blocks with the set screw. FYI - if you crank hard on the set screw you can deform the inside bore of the barrel (been there, done that - that's why we use clamp on blocks for all our build ups).

Robert