AR Feed Problem

[MtnBksRCul]

I have an AR rifle that I assembled from parts. It has functioned flawlessly with several different types of ammunition. Last time I went shooting, it worked fine for the first 60 rounds through it, but when I switched to a different, new ammunition that I had purchased, the ammunition would not feed. This was the first time I had used this ammunition.

The malfunction happened as follows:

The 1st round would load normally upon releasing the bolt. When that round was fired, instead of the next round feeding normally, the tip of the round would jam into the upper locking lugs of the breech above the chamber. The bolt was picking the round up properly (not short stroking). I could either pull the charging handle back about 3/4" and the round would drop in and feed into the chamber when I released the charging handle, or, if I pulled the charging handle back all the way, it would create a double feed and I would have to drop the magazine to clear.

The ammunition was Independence XM1931 55 grain 5.56x45.

My rifle has:
PSA lower (M-4 feed ramps)
VLTOR MUR upper
Spikes Tactical nickel/boron bolt and carrier
Daniel Defense Barrel (M-4 feed ramps) 16" mid length gas
VLTOR low profile gas block
VLTOR A-5 7 position buffer tube
VLTOR A-5 buffer spring and buffer (H-2)
Magpul Gen 3 10 rd magazines

This malfunction was very consistent. It happened at least 90% of the time a round was fired.
The rifle was cleaned with Froglube the night before.
The ammo is the primary suspect, however, the spent casings do not show any obvious signs of dangerous overpressure.

One other guy had the same ammunition and was having issues as well. Unsure as to how his rifle was malfunctioning, specifically.
The rounds worked fine in my AR pistol (Adams Arms piston set up, 7.5" barrel)
The rounds also worked fine in another guys AR.

The only thing I can figure is that the rounds were a bit hot and were causing the bolt carrier and buffer to cycle a bit too fast causing the bolt to pick the next round up a little too harsh and the tip of the round was bouncing off the feed ramp into the top of the breech/locking lugs.

I think that a heavier buffer might help with this issue (I still have about 840 of these rounds). The rounds work fine in my pistol, however, I'd like to be able to use them in my rifle as well.

Any thoughts?

[sl0re10]

unburned powder is my guess... which is ammo related / specific (re: not the rifle causing).

Should only be dust and grime (dust mixed with oil) left over from firing. If there is anything that looks like gun powder in your gun its not fully burned powder that gets in the way of the bolt closing (and/or of the rounds chambering). Heavier spring wouldn't fix this... if that what it is.

[MtnBksRCul]

unburned powder is my guess... which is ammo related / specific (re: not the rifle causing).

Should only be dust and grime (dust mixed with oil) left over from firing. If there is anything that looks like gun powder in your gun its not fully burned powder that gets in the way of the bolt closing (and/or of the rounds chambering). Heavier spring wouldn't fix this... if that what it is.

The only thing keeping the bolt from closing is the tip of the round going into the upper locking lugs of the breech instead of into the chamber. The round is not feeding into the chamber when the bolt picks it up and pushes it. The tip of the round is jumping over the chamber and into the upper locking lugs where the bolt rotates and locks to the back of the chamber assuming the round goes where it is supposed to. The rifle was relatively clean when this started happening (60 rounds of a different ammo through it before the ammo change/malfunctions started). The only residue is normal carbon fouling that any direct impingement AR will experience. The bolt was not binding and was cycling quite freely. This was not a friction issue where fouling was causing binding. The round was tipping up at about a 45 degree angle and hopping over the top of the chamber, creating a mechanical lock up (the only way the bolt could move forward is by crushing/deforming the round).

As I stated before, the ammunition is definitely a component of the problem. The rifle has functioned flawlessly with several other types of ammunition. It does not like this particular brand. That being said, I have over 800 rounds of this particular brand. If I can swap out the buffer (not the spring) and make it work, it's a fairly cheap fix. I've been intending to try a heavier buffer anyway. If it doesn't work, I can use the rounds in question for my AR pistol, which seems to eat them just fine. However, that means I have to go buy more rounds for my rifle and I had not intended to do that for a while as I had just purchased this batch of 1000 rounds.

[sl0re10]

The only thing keeping the bolt from closing is the tip of the round going into the upper locking lugs of the breech instead of into the chamber. The round is not feeding into the chamber when the bolt picks it up and pushes it. The tip of the round is jumping over the chamber and into the upper locking lugs where the bolt rotates and locks to the back of the chamber assuming the round goes where it is supposed to. The rifle was relatively clean when this started happening (60 rounds of a different ammo through it before the ammo change/malfunctions started). The bolt was not binding and was cycling quite freely. This was not a friction issue where fouling was causing binding. The round was tipping up at about a 45 degree angle and hopping over the top of the chamber, creating a mechanical lock up (the only way the bolt could move forward is by crushing/deforming the round).

yeah; I was seeing deformed bullets too. I cleaned my feed ramps a couple times thinking there was a relationship...

but I was also seeing grey powder sticks around (including on the shooting bench). Also easy to notice / see places like in the mag well.

and it didn't go away until I cleaned everything including the bolt on in the inside by blowing some canned remoil through it.

The problem spread to a friend's rifle too as he used the ammo that wasn't burning powder well. and it persists even after stopping using the bad ammo / until the really good cleaning.

[nate76239]

You already have an H2 buffer which is heavier than standard. I have used this ammo on a 20 inch barrelled upper with rifle length gas system and rifle buffer and I get short stroking where the round is fired but it doesn't grab the next round. The rifle works fine with federal xm193 and m855. I used the Independence ammo on other rifles with both midlength and carbine gas systems with no problem, those had a standard carbine buffer. I would suggest trying the buffer from the AR pistol which doesn't experience this problem.

[Bullets&Whitewalls]

Did you try going back to another ammo type? What type of mags? Could the feed lips on the mags be worn enough to let the round pop out pre mature? Or maybe the cases are a different size? I know these are reaching questions but your issue has peaked my curiousity.

[tal3nt]

It's the H2. Go standard carbine

[MtnBksRCul]

yeah; I was seeing deformed bullets too. I cleaned my feed ramps a couple times thinking there was a relationship...

but I was also seeing grey powder sticks around (including on the shooting bench). Also easy to notice / see places like in the mag well.

and it didn't go away until I cleaned everything including the bolt on in the inside by blowing some canned remoil through it.

The problem spread to a friend's rifle too as he used the ammo that wasn't burning powder well. and it persists even after stopping using the bad ammo / until the really good cleaning.

I'm not getting deformed bullets or signs of unburned powder. The reason I mentioned bullets deforming is that the jammed round was in a position where it would require deforming or smashing the round to move the bolt forward. If the bolt is manually moved to the rear 3/4" , the round falls into place and will then insert into the chamber normally and fire, leading to the next round doing the same thing.

The magazines are relatively new. The rifle/magazines/ammunition were working fine through the first 60 rounds that day. The malfunctions started when I changed to a different ammunition that I had never used before. The cause is not in question, it's the ammunition. What I am trying to find is a way to use said ammunition since I still have over 800 rounds of it.

Also, the VLTOR A5 H2 buffer is not the same thing as a standard carbine H2 buffer. An A5 H2 buffer is standard weight for my buffer system. An A5 H2 buffer is not compatible with a standard carbine buffer tube, nor is a standard carbine buffer of any weight compatible with my A5 buffer tube.

From VLTOR's website:

"1. Can I use these buffers in a carbine receiver?

No, the VLTOR A5 buffers are only designed to work with the A5 receiver extensions (RE-A5 and RE-10/A5SR). Attempting to use these parts in a regular carbine receiver extension will result in damage to the firearm and potential injury to the operator."

I would have gone back and tried a different ammo if I had any. However, I did not. I may be able to try some this weekend.

As far as the cartridge cases being slightly different sized, I don't know. The ammunition was new, not reloaded. I would hope it meets industry standards. My understanding is that Independence ammo is under the Federal/IMI umbrella.

[FeuerFrei]

My experience with this ammo suggested that it is low powered like Wolf and PMC-A load. It will go bang and feed if you tune your rifle for it.
Try a lighter buffer.


Sent using a long string & 2 cans.

[nate76239]

I was double checking your setup and the Vltor A5 buffer and tube are proprietary so you can only go with another Vltor A5 buffer. The Vltor H2 is 5.3 oz, which is slightly heavier than a standard rifle buffer 5oz, the standard carbine buffer is 3oz. I think you might be too heavy on the buffer for the weaker ammo. Vltor makes a lighter H0 and H1 buffer. Hopefully there's a calgunner with an A5 buffer near you that can help troubleshoot.

[MtnBksRCul]

I was double checking your setup and the Vltor A5 buffer and tube are proprietary so you can only go with another Vltor A5 buffer. The Vltor H2 is 5.3 oz, which is slightly heavier than a standard rifle buffer 5oz, the standard carbine buffer is 3oz. I think you might be too heavy on the buffer for the weaker ammo. Vltor makes a lighter H0 and H1 buffer. Hopefully there's a calgunner with an A5 buffer near you that can help troubleshoot.

That is correct, and the A5 H2 buffer is the standard (not heavy) weight for this set up. I am fine with buying a lighter and/or heavier buffer (I have already purchased a heavier buffer).

To me, it seems that if the ammunition was underpowered, the bolt would not move back far enough to pick the round up and either not move the round out of the magazine at all or it would pinch the round on the side and move the round partially out of the magazine. The bolt is travelling far enough to the rear to pick the round up properly.

[Nomadfisher626]

This is the essence of the AR platform. Freaking out on deployment that my rifle was literally going to get me killed. Clean clean clean clean clean every opportunity and I never ran it dry always a semi wet bolt. And small bottle of CLP handy for. When the inevitable failure to feed drill would need to be executed.

[MtnBksRCul]

This is the essence of the AR platform. Freaking out on deployment that my rifle was literally going to get me killed. Clean clean clean clean clean every opportunity and I never ran it dry always a semi wet bolt. And small bottle of CLP handy for. When the inevitable failure to feed drill would need to be executed.

The rifle was fairly clean (60 rounds through it after a good cleaning. I was taught by the Marine Corps how to clean a rifle) and well lubricated (with Frog Lube, not compatible with CLP). The rifle is also fairly new (between 500-1000 rounds through it), not used and abused like military service weapons are.

Again, the issue is the rounds. I'm just trying to find a solution to get the rounds to work. It seems that a few people think they are underpowered, while I thought they might be a bit hot.

[96chevjumps]

I have ran this ammo out of a 18" rifle length gas system barrel using a H buffer with no issues. Its hotter than pmc thats for sure. Shoots clean and pretty accurate.

What ammo did you use that was functioning in your rifle before the issues started?

[nate76239]

That is correct, and the A5 H2 buffer is the standard (not heavy) weight for this set up. I am fine with buying a lighter and/or heavier buffer (I have already purchased a heavier buffer).

To me, it seems that if the ammunition was underpowered, the bolt would not move back far enough to pick the round up and either not move the round out of the magazine at all or it would pinch the round on the side and move the round partially out of the magazine. The bolt is travelling far enough to the rear to pick the round up properly.

Let us know how the other buffer turns out. I definitely understand that it's not short stroking what I'm thinking is that the cyclic rate is slower and it may not be feeding the round fast enough/slamming it home.