Diagnose my AR Malfunction

[Mass-diver]

Although I own a couple rifles, I'm more of a pistol guy and I'm pretty clueless with lots of rifle issues, so I'm looking for someone to diagnose this problem with my AR.

Here's what is going on: new upper. 1st time at the range, first round fires, casing ejects clean, I go to pull the trigger and it has not reset (cocked). The second round is in the chamber and ejects (unfired) when I pull the charging handle. This pattern of a clean feed but the the rifle not being cocked is repeated over the next 20 rounds. Then I fire 60 more rounds with no malfunctions.

I took the rifle home and lubed the BCG. Yesterday I went back to the range, the first round fired and ejected, but the trigger did not reset (although again, round 2 was in the chamber). I fired 80 more rounds with zero malfunctions.

Anyone experience a similar problem? The main issue is that I'm falling in love with this rifle and I shoot it better than anything else I own. But, I was raised by a Father who had a very low tolerance for weapons that malfunction and he has ingrained it my head that if something isn't close to 100% reliable, it is useless.

Any comments would be much appreciated!

 

[RickG]

Are you using factory ammo? Did you try with a different mag? You mentioned that it was a new upper, do you have the original and does it work ok? My first inclination would be to check the ammo. It sounds as though your ar is short stroking but it could be a problem with your carrier not making good contact with the hammer and riding over it.

Interesting problem. I am interested in what others have to say as well.

 

[Mass-diver]

Are you using factory ammo? Did you try with a different mag? You mentioned that it was a new upper, do you have the original and does it work ok? My first inclination would be to check the ammo. It sounds as though your ar is short stroking but it could be a problem with your carrier not making good contact with the hammer and riding over it.

Interesting problem. I am interested in what others have to say as well.

Same ammo, both times (PBC), I did switch mags, but all my mags are pretty beat up. I don't have the original upper.

 

[andy t]

who made the upper, lower? Was the lower complete or did you install LPK yourself?

 

[lord1234]

It coudl also be that your mags are not fully feeding. What happens if you hand feed one round at a time?

 

[Mass-diver]

who made the upper, lower? Was the lower complete or did you install LPK yourself?

The upper is a Delton kit. The lower is an old preban DPMS. I bought the lower complete and sold the old upper. The only thing I did to the lower was install a Mag-Pul collapsible stock (with a carbine buffer and spring).

 

[Mass-diver]

It coudl also be that your mags are not fully feeding. What happens if you hand feed one round at a time?

I haven't tried that, good idea though. Again, the weird thing is, the problem seems to go away after a few rounds. You would think that if something didn't line up right that I would not be able to fire 78 rounds without issue?

BTW, GREAT avatar

Here's a pic (just to make the thread more interesting) of the ol' jammomatic

 

[Junglerott]

Are there any wear marks on the BCG?

 

[Mass-diver]

I there any wear marks on the BCG?

No the BCG looks OK (brand new), but the the lower certainly has some wear marks.

 

[doobie]

Is the bolt pulled back when you seat the mag? If the bolt is closed the mag won't seat properly.

 

[Junglerott]

Maybe the spring needs to break in a little? It sounds like your more recent trip was a lot better.

 

[Mass-diver]

Is the bolt pulled back when you seat the mag? If the bolt is closed the mag won't seat properly.

hmm, not sure about that......

Of course, I'm going to try to go back to the range asap. Things would be easier if it was like the old days (pre-panic, pre ammo bubble) and I could put a couple hundred rounds down range.

Thanks again to everyone for all the comments so far.

 

[icyclefar]

I'm assuming everything is cleaned and lubricated ...........

Are you loading the mags to full capacity?

If you've got 30 rounds in a 30 round mag you may have too much resistance when round two peels out of the mag, leaving your rifle just slightly out of battery.

Did you try the forward assist?

Try putting 5 or 10 rounds in a mag, then move up to 25 and see if the problem still occurs.

 

[lord1234]

hmm, not sure about that......

Of course, I'm going to try to go back to the range asap. Things would be easier if it was like the old days (pre-panic, pre ammo bubble) and I could put a couple hundred rounds down range.

Thanks again to everyone for all the comments so far.

Nothing says you can't. Just might cost you a bit more

 

[Mass-diver]

I'm assuming everything is cleaned and lubricated ...........

Are you loading the mags to full capacity?

If you've got 30 rounds in a 30 round mag you may have too much resistance when round two peels out of the mag, leaving your rifle just slightly out of battery.

Did you try the forward assist?

Try putting 5 or 10 rounds in a mag, then move up to 25 and see if the problem still occurs.

I've only been shooting 3-5 rounds at a time (range rules )

I'm gonna try some different mags.

In terms of ammo, it's not just the cost, my local gunshop will only sell me 2 boxes at time. Hell, I had to spend 5 bucks on a fake mustache just to get two more boxes last week

 

[hminsky]

Take apart the trigger group and look for a primer that has gotten stuck down in there someplace at the bottom.

 

[zerodown]

Sounds to me like its something with the lower parts. You can start by pulling the rear pin and checking where the hammer locks to the trigger bar. Check for wear and try pushing the hammer down by hand to see when/if it engages. Snap it back together and try pulling the charging handle slowly and see if it engages 100% of the time. The BCG only has to move 1/2 rearward for the hammer to reset so if its loading the next round, its definitely moving far enough to engage the hammer. My guess is that one of these is worn down. Next time you are at the range, if it fails to fire, clear the gun, split it and check to see if the hammer is reset. I'll bet that it isn't and the reason you are able to fire sometimes is that there may be just enough to hold the hammer part of the time or after a couple rounds, some crud is building up.

Icyclefar is also right - If it isn't the lower parts then the BCG isn't going completely to battery. Make sure the chamber and bolt are all clean. The forward assist can give it that extra push that it may need.

 

[ScottS]

Sounds to me like its something with the lower parts. You can start by pulling the rear pin and checking where the hammer locks to the trigger bar. Check for wear and try pushing the hammer down by hand to see when/if it engages. Snap it back together and try pulling the charging handle slowly and see if it engages 100% of the time. The BCG only has to move 1/2 rearward for the hammer to reset so if its loading the next round, its definitely moving far enough to engage the hammer. My guess is that one of these is worn down. Next time you are at the range, if it fails to fire, clear the gun, split it and check to see if the hammer is reset. I'll bet that it isn't and the reason you are able to fire sometimes is that there may be just enough to hold the hammer part of the time or after a couple rounds, some crud is building up.

I agree. I'm guessing this is a lower problem, not an upper problem. If I understand the problem correctly, the spent round extracts/ejects cleanly, and the new round chambers correctly, with the rifle returning to battery, but the hammer is not resetting. That localizes the problem to the lower, rather than the magazine, BCG, upper, etc.

How worn is the lower? Know anything about the LPK in it?

ETA: one easy to more speficically localize this problem. Next time it happens (i.e. you pull the trigger and nothing happens), hit the forward assist and then pull the trigger again (muzzle pointed in a safe direction, of course.) If the hammer drops, the weapon was slightly out of battery, and that's the reason for the hammer not falling. Now you're looking at badly resized ammo, dirt, BCG issues, etc. If you hit the FA, pull the trigger, and the hammer still does not fall, then you're most likely looking at the lower.

 

[Mass-diver]

Thanks again for the advice by everyone, I going to keep everything in mind when I hit the range this weekend. I think you guys are right that the lower is probably pretty warn, it looks like it is probably the original kit in the lower. I've been thinking about getting a new trigger kits installed, so If this continues to look like the possible issue, maybe I'll just have the whole lower kit replaced?

 

[economist]

I would expect hammer follow to result in full-auto or at least a double tap now and then. So, I am guessing the hammer is cocked but the trigger is not resetting. That implicates the trigger spring. Take off the upper and cock the hammer while pulling the trigger back. Slowly let off the trigger. It should spring forward with a little click. If it does not, the trigger spring is weak or installed incorrectly.

 

[abomb60]

It's also possible that you might be having a gas pressure problem. The bolt carrier could be moving far enough back to eject the round but not be going far enough back to get a new round or recock the hammer.

When the problem happens do you get a click & no bang or is there a new round in the chamber? If there is no new round in the chamber it's not an issue with your lower. If there is a new round and you don't get a click it could still be an issue with the lower or upper.

 

[Mass-diver]

It's also possible that you might be having a gas pressure problem. The bolt carrier could be moving far enough back to eject the round but not be going far enough back to get a new round or recock the hammer.

When the problem happens do you get a click & no bang or is there a new round in the chamber? If there is no new round in the chamber it's not an issue with your lower. If there is a new round and you don't get a click it could still be an issue with the lower or upper.

First round fires, ejects clean, I go to pull the trigger for the next shot, there is no click, the trigger is not cocked (it is in the far back position and can not be pulled). There is a live round in the chamber.

 

[abomb60]

First round fires, ejects clean, I go to pull the trigger for the next shot, there is no click, the trigger is not cocked (it is in the far back position and can not be pulled). There is a live round in the chamber.

So it could be either a spring issue or the carrier isn't coming back far enough to grab the hammer and bring it back all the way. I would try replacing the gas tube and gas rings (shouldn't be more than $12 in parts).

I once had a similar issue and tried cleaning the gas tube but it turned out that it was worn at the end where it meets the gas key causing a pressure leak. Oh and speaking of gas keys make sure it's still nice and tight against the carrier.

- Adam

 

[MassMark]

I was going to suggest a loose carrier key as well that settles in as the gun heats up....

 

[Mass-diver]

Will check the carrier key for sure

 

[economist]

The thing is, you can't get a new round into the chamber without the carrier coming back enough to cock the hammer. The hammer cocks when the bolt face is about half-way over the mag well. So, if you have a live round and no trigger reset then gas is not your primary problem. The problem is either the hammer not being caught on the way back and then following the carrier and live round forward (unlikely, given no bang at this point) OR the trigger is not being reset. This means that the most likely source of the problem is in the lower, and that the first place to look is the trigger spring. See my earlier post on how to check.

 

[abomb60]

The thing is, you can't get a new round into the chamber without the carrier coming back enough to cock the hammer. The hammer cocks when the bolt face is about half-way over the mag well. So, if you have a live round and no trigger reset then gas is not your primary problem. The problem is either the hammer not being caught on the way back and then following the carrier and live round forward (unlikely, given no bang at this point) OR the trigger is not being reset. This means that the most likely source of the problem is in the lower, and that the first place to look is the trigger spring. See my earlier post on how to check.

You make a good point

Any chance the OP has access to another working lower to try his upper on?

 

[andy t]

Trying a different lower with the same upper would def help. However, I would just get a new LPK which will most likely resolve any issues.

 

[Mass-diver]

The thing is, you can't get a new round into the chamber without the carrier coming back enough to cock the hammer. The hammer cocks when the bolt face is about half-way over the mag well. So, if you have a live round and no trigger reset then gas is not your primary problem. The problem is either the hammer not being caught on the way back and then following the carrier and live round forward (unlikely, given no bang at this point) OR the trigger is not being reset. This means that the most likely source of the problem is in the lower, and that the first place to look is the trigger spring. See my earlier post on how to check.

I did this test per your earlier post and felt a click when I released the trigger. I'm pretty sure I did the test as you indicated.

In terms of another lower, the only other one I have is post-ban, and knowing my luck......

I think I'm going to mess around with the upper one or two times and then if I'm still having trouble I'll replace the whole LPK. It's old and the trigger doesn't feel that great anyways (versus other ARs that I have owned).

Thanks again for all the advice so far. It's sort of an odd ball malfunction and it really seems to get better as the rifle warms up, but then again it's hard to say for sure since I'm only shooting relatively low round counts.

 

[Mass-diver]

Trying a different lower with the same upper would def help. However, I would just get a new LPK which will most likely resolve any issues.

If only this was a year ago and these were easy to order