Issue with AR15 not cycling

[Whisker]

So I have an Armalite A4 that has probably close to 2,000 rnds through it.

In the early days, I had no problems whatsoever with it.  Now, the rifle functions mostly like a semi auto.

The first round fires, and ejects the brass.  The second round does not chamber.  But the hammer is reset so I can dryfire the second shot.

What's going on likely?

Simply a worn out rifle?  I doubt it, right?
Dirty chamber that I cannot clean using normal methods?
Dirty gas tube, or one that needs adjustment?  If so, where is a tutorial of how to fix that?
Could it be the buffer spring?
Or some sort of O-ring on the bolt?

[eaglescouter]

1.  Are the o-rings still present on the tail of the bolt?
2.  Is the gas tube still firmly staked in place at the gas block?

[techres]

1. Try a new magazine.  Could be dying spring in old mag.
2. Check to see if it is short stroking (I.E. not going back far enough to catch the lip of the next round - look for scratches in the brass).
3. Look for soot around the gas block to see if you have a leak.
4. Check the staked nuts and see if they are loose.
5. Try different ammo.
6. Use a 2nd AR to test the upper and bolt carrier group separately to isolate down.

Good luck!

[Whisker]

1.  Are the o-rings still present on the tail of the bolt?
2.  Is the gas tube still firmly staked in place at the gas block?

1.  Yes there are o-rings on the back of the bolt.  They are wiggly, but from what i know that is normal.  When manipulating them, they will extend about a millimeter from the the bolt.

2.  Yes, the gas tube seems firm at the gas block. 

[Whisker]

1. Try a new magazine.  Could be dying spring in old mag.
2. Check to see if it is short stroking (I.E. not going back far enough to catch the lip of the next round - look for scratches in the brass).
3. Look for soot around the gas block to see if you have a leak.
4. Check the staked nuts and see if they are loose.
5. Try different ammo.
6. Use a 2nd AR to test the upper and bolt carrier group separately to isolate down.

Good luck!

1.  Seems to be consistent with most magazines. 
2.  Yes, I think this is the essence of the problem.
3.  No soot visible
4.  staked nuts?  Do you mean castle nuts?  Your question did prompt me to inspect the hand guard retaining ring and notice a wavey movable disk behind the hand guard retaining ring.  It kind behaves like cardboard.  Never noticed it... wonder if it's normal?
5.  Tried different ammos with same result
6.  will do. thanks.

[techres]

4.  Are these nuts loose?  (pic below)

[mtmisfit]

remove the buffer spring and buffer, clean the buffer tube, spring and buffer and make sure the vent hole in the stock retaining screw isn't plugged.

Inspect the buffer/tube for wear and any place the buffer or bolt carrier may be dragging. Is the carrier hitting the buffer retaining pin?

Is the hammer dragging on the bottom of the bolt?  Is there something under the trigger/hammer/disconnector assembly binding?

If it's short stroking with full power ammo, of different types and it's not mag related, check to see if your front sight base has moved and is no longer aligned with the gas port. (unlikely)

Is the carrier key still tight? (re:staked nuts) look at an AR parts diagram.

Are you running it wet? (plenty of lube)

The wavy washer in the delta ring is normal, that's the spring that keeps the handguards on. (the one you swear at taking the handguards off)

[mtmisfit]

techres,

Whose carrier is that? (brand)

Like the finish, don't like the stake job on the carrier key though.

mtmisfit

[azmule]

The second round doesn't get stripped off the top of the magazine at all, i.e. the bolt just rides over it and closes empty?  Does this happen with every mag?  When cycled by hand does it feel totally smooth all the way back with no sticky spots?  If so I'd check for leaks or partial blockages in the gas system.  Do the new ones use an O-ring on the bolt now?  The only ones I'm familiar with use 3 steel piston style rings, each with a small gep to allow them to expand against the cylinder, and sometimes they could rotate so that the gaps would align and allow gas to escape, those gaps should be evenly spaced apart.  If that's been replaced by something different than my knowlege is out of date and I need to dig into a newer model soon.   

[techres]

techres,

Whose carrier is that? (brand)

No idea.  Borrowed from google images to circle what is hard to describe in words.

[Caliper]

Does the bolt lock back after the last shot? 

[Whisker]

Does the bolt lock back after the last shot?

No it does not generally. 

[techres]

Yep, short stroke.

If nothing else has helped, I have in taken off the upper, removed the bolt carrier group, pointed the barrel at the ground and spray carb cleaner right down the gas tube using the plastic tube most carb cleaners come with.  Spray enough that the gunk flows down and onto the ground.

Then run an AR pipe cleaner through the tube as much as possible or just blow some compressed air down it, or just let it dry.

DO NOT GET THE CARB CLEANER ON ANYTHING PLASTIC OR IT WILL GET EATEN.
Also the carb cleaner can give a weird stain to the upper if you get it all over (whitish).

This can help increase gas pressure and sometimes helps.  Worth a shot if you have done all of the other things people have suggested.

[ItsanSKS]

Found the same exact problem on a good friends rifle, an Armalite HBAR.  Wouldn't do it consistently, but enough to be annoying.  Determined that the rifle, which would, when new, eat *anything* now required mil-spec ammo to function 100%. 

Through handload developement procedures, we determined that any 55gr load that achieved less than 3100 fps 10' from the muzzle would get about a 10% failure rate, resulting in the situation you describe.

Loads that were in excess of this velocity functioned flawlessly.

Specific commercial ammo that caused this problem: 55 PMC Bronze

[Shooter30-06]

My Bushmaster had the identical problem with Remington factory ammo.  Handloads with magnum small rifle primers work like a charm.

[ItsanSKS]

My Bushmaster had the identical problem with Remington factory ammo.  Handloads with magnum small rifle primers work like a charm.

Out of curiosity, are you also using a 'ball' powder, such as H335?

[techres]

Specific commercial ammo that caused this problem: 55 PMC Bronze

^This

Same thing that I found.  I also found that flinching shooters increased the issue as well as those that do not really put their shoulder into it.  Obsessive cleaning gets it over the hump (which is why I mentioned it before) and so does switching to federal or other milsurp.

[Shooter30-06]

I use H335 and IMR4198. 

[RangeRat]

Radway would cause this in my and a buddy's AR.  We found them to be running a little too dry for this underpowered ammo and unlocking too slowly.  In your case try cleaning the inside of the bolt carrier (scrape carbon out) and relube the inside of the carrier.  Unless one of the new uber coatings is being used, lube well.... and not with CLP! 

Did you get a chance to try the carrier group in another rifle?

RR

[VietVet]

 As already stated "Short Stroking".
I have several AR's. Due to ammo costs I purchased some Wolf 223.
One of my AR's would not cycle correctly using this ammo. All the others would do just fine. For whatever reason the 20" barrel would short stroke with Wolf. Longer gas tube, not enough pressure to send the bolt completely back to pick up the next round. Without going back and reading all the recommended solutions my guess is either a dirty gas system or bad ammo.

[Mark Davis]

Nobody mentioned worn gas rings.
If your rifle is a bit rough inside the bolt carrier where the gas rings seal, your gas rings can wear out in 2000 or so rounds.
To test that theroy, put a drop of oil on the rings (through the hole in the bolt carrier) If you acheive function for a few rounds then short stroke again after the oil is burned off, replacing the rings should fix the problem.
Most rifles do not have a problem with gas ring wear.
Some do.
My apologies to whoever mentiond O rings. That terminoligy make me think rubber.

[Spartan]

 A rare occurence can be that the roll pin up front that secures the gas tube actually comes lose and can even come out. This will cause exactly the symptoms you are describing along with off call shots. When you check the gas tube for tightness, you have to take the handguards off and see if it was firmly in place and verify that the roll pin is infact in there.

[Whisker]

6. Use a 2nd AR to test the upper and bolt carrier group separately to isolate down.

Good luck!

Okay so got around to doing some diagnostics with another AR.

Used 20" Bushmaster.

Swapped some stuff around.

First tested to see if the Bushmaster (B) worked okay on its own.  Check.
Put my Armalite (A) bolt in the Bushmaster (B) rifle.  Worked fine
Put (A) lower and bolt on (B) worked fine.
Put (B) bolt in (A) and had some of the same malfunction.
Put (B) Lower and Bolt on (A) upper.  Malfunction every time.

So it's my (A) Armalite upper.

So what do you think?  Is there some way to get around dropping $ at an Armorer?

Thanks again

[Whisker]

Yep, short stroke.

If nothing else has helped, I have in taken off the upper, removed the bolt carrier group, pointed the barrel at the ground and spray carb cleaner right down the gas tube using the plastic tube most carb cleaners come with.  Spray enough that the gunk flows down and onto the ground.

Then run an AR pipe cleaner through the tube as much as possible or just blow some compressed air down it, or just let it dry.

DO NOT GET THE CARB CLEANER ON ANYTHING PLASTIC OR IT WILL GET EATEN.
Also the carb cleaner can give a weird stain to the upper if you get it all over (whitish).

This can help increase gas pressure and sometimes helps.  Worth a shot if you have done all of the other things people have suggested.

Carb cleaner... Do you mean carbon cleaner? Or like auto carburetor cleaner?    Seriously, just want to clarify.

[oladcock]

So some of you guys clean gas tubes? Besides all mentioned above, I'd look at buffers and springs being too heavy, too strong, or dirty/hanging up........O.L.

[Whisker]

So some of you guys clean gas tubes? Besides all mentioned above, I'd look at buffers and springs being too heavy, too strong, or dirty/hanging up........O.L.

Yeah... but I don't see how my springs and buffers would strengthen over the years.

[techres]

Carb cleaner... Do you mean carbon cleaner? Or like auto carburetor cleaner?    Seriously, just want to clarify.

auto carburetor cleaner - yep

It is not a preferred method because it is only going to give you small percentages of extra reliability and as soon as the thing gunks again you will be back in trouble.

That being said, I have seen it help before and is not an expensive test. to try.

If the problem is isolated to the upper, then the issue must be at either the gas tube/gas block or at the chamber.  The cleaner can help with the tube.  The gas block would be an issue if you had leaking due to a shift in it - but this usually leaves a nasty smoke on the barrel around the gas block that you can see on a SS barrel or pick up with a rag/patch on a dark barrel.  If this is it then you will have to have the block re-mounted.

If it is the chamber then any gunsmith should be able to help, or give armalite a ring.

At least you have it isolated down.

[techres]

So some of you guys clean gas tubes?

Normally?  No.
In a pinch?  Yes.
Should you have to?  Oh, absolutely not.

[jrturbo]

I would definitely try at least compressed air through the gas tube.  Could have carbon / jacket material blocking the gas port in either the barrel or the gas block.  Also make sure that your gas block didn't move and partially block the gas port in the barrel.

Turbo.

[hinermad]

Yeah... but I don't see how my springs and buffers would strengthen over the years.

Really dirty springs can be so clogged they won't compress as far as they used to. The force doesn't really change, but the amount of travel can.

Dave