Failure to Feed; Was Failure to extract

[Iraqgunz]

The mags. If that ammo is working in other mags with no more malfunctions, with exception of the D&H mags, I would have to assume they are the issue. Unless I misread your post.

The mags or the ammo? Or both? I'm also concerned something is awry with the upper...anything to look for on the upper that could cause this?

[gaijin]

I have also experienced feed issues with D&H mags.
They are relegated to "practice mag" status, if they're used at all.

Add-I've never experienced feed issues with IMI m193 with Pmags and Brownells mags.
I've shot several cases of it.

[tehpwnag3]

Mark all of your mags for identification. When a pattern emerges, you won't be pulling your hair out in frustration.

[LMT/556]

I had failures to feed that were a result of a loose gas key (Centurion Parts), what would happen is occasionally the carrier wouldn't travel rearward enough to get the bolt behind the next round, it was the BCG leading edge that caught the next round resulting in a hard angle into the chamber with the bolt jamming into the side of the cartridge. Sometimes it would cycle fine, sometimes it would not go back far enough to strip the next round, and sometimes it would strip the round with the BCG and the bolt would smash the round. Usually there wasn't enough energy to lock the bolt back last round either, very inconsistent until the gas key was tightened down. Gas key might not be your problem but I'm still thinking it's an undergassed situation causing your trouble.

My mags of choice are Okay mfg, NHMTG mostly with my favorite the 20 rnd variety. DH stamping places a folded metal edge into the side of the cartridge of one of the top rounds, though honestly I never had any feeding issues in my limited use.

I experienced feeding issues with a pair of NHMTG 20 round mags which ended up being the springs were installed upside down which compromised the follower. Flip and installed correctly and that problem went away.
IMG_20160321_162342_523.jpg

[nightchief]

I had failures to feed that were a result of a loose gas key (Centurion Parts), what would happen is occasionally the carrier wouldn't travel rearward enough to get the bolt behind the next round, it was the BCG leading edge that caught the next round resulting in a hard angle into the chamber with the bolt jamming into the side of the cartridge. Sometimes it would cycle fine, sometimes it would not go back far enough to strip the next round, and sometimes it would strip the round with the BCG and the bolt would smash the round. Usually there wasn't enough energy to lock the bolt back last round either, very inconsistent until the gas key was tightened down. Gas key might not be your problem but I'm still thinking it's an undergassed situation causing your trouble.

A gas issue is possible, however, the FTF's happened using two different carriers, an LMT enhanced and a Sionics carrier. ALso, the weakest ammo, the PMC Bronze, cycled 100%. It's the hottest ammo, the IMI 556 that wouldn't feed.

My mags of choice are Okay mfg, NHMTG mostly with my favorite the 20 rnd variety. DH stamping places a folded metal edge into the side of the cartridge of one of the top rounds, though honestly I never had any feeding issues in my limited use.

I have some of the Okay mags too, and will try them with the IMI 556 to see how they do. I'll also try the IMI 556 in a different rifle with the DH mags to see if they still cause the feed ramp slamming.
Interesting to me that I only get the failures with the DH mags and the IMI 556. DH mags with PMC Bronze, GECO and AE all fed without issue.


NC

[nightchief]

Mark all of your mags for identification. When a pattern emerges, you won't be pulling your hair out in frustration.

All mags are marked. This issue happened with all four of the DH mags I was using, but only the IMI 556 cartridges. I ran a mixture of G2 and G3 Pmags, probably 10 different mags and didn't have any feed issues with any of the pmags.

[BufordTJustice]

All mags are marked. This issue happened with all four of the DH mags I was using, but only the IMI 556 cartridges. I ran a mixture of G2 and G3 Pmags, probably 10 different mags and didn't have any feed issues with any of the pmags.

I run my 11.5" RGP with a significantly restricted SLR gas block, A5H4 buffer, LMT e-carrier, and tubbs AR10 flat wire spring (roughly the same strength as a sprinco green, which I also have). I use either gen 3 pmags or Lancers.

Mine works fine using IMI 55gr or Federal Brown box XM193.... suppressed or unsuppressed. Just adding this for a data point.

I think you're on the right track with looking at the mags, brother.

Sent from my SPH-L720T using Tapatalk

[BLACKMAX1]

I built a new upper for suppressed use using the Sionics 11.5” reduced gas port barrel. I function tested today unsuppressed (suppressor still in NFA jail) running a BCM bolt with LMT E-Carrier and Vltor A5 RE, Sprinco green spring and A5H2 buffer. Test was run on a Seekins forged lower with 2500+ rounds run. First 40 rounds through went with no issue. GECO 223 55gr FMJ was fired on approximate 2 second intervals.

Next, I ran some basic movement drills shooting at a much faster pace. IMI 556 55gr FMJ, Wolf Gold 223 55gr FMJ and American Eagle 223 55gr FMJ were used in various Gen 2 and Gen 3, 30 round pmags that have run hundreds of rounds with out issue.

About four to five mags into these drills, as the gun got hot, I started to get failure to extract malfunctions. The first failure to extract was with IMI 556, the remainder of the malfunctions were with the AE 223 rounds.

I was anticipating possible short stroking/failure to lock, but this malfunction doesn’t appear to be that. I changed out the BCM/LMT BCG to a BCM built BCG with several hundred rounds run and the malfunction appeared to go away, however, I was out of the AE ammo after running 20 rounds. Wolf Gold and GECO ran with out issue using the BCM BCG. The ejection pattern with both BCG's was consistent and about 4 o'clock.

Outside air temperature was 87 degrees.

Need some advice on what changes to make to isolate the issue. I don’t think there is a gas flow issue at the gas block, as the barrel is pre-drilled and a BCM low profile gas block with set screws was used and appears to be installed properly. Similar situation with the gas tube.

Thank you.

Nightchief

Attachment 45146Attachment 45147Attachment 45148Attachment 45149

Scionics website says that the reduced gas port barrel may not cycle properly when ran without a suppressor. FWIW

[nightchief]

So I went out for another function test today. Tried IMI in DH, Lancer, Okay and Pmags. As the gun got hotter, I started to have more trouble with the failures to feed. It occurred in the DH and Okay mags. I used these same mags, with this ammo, in my other SBR, with BCM built upper. No feed issues in the BCM. I do not believe it is the mags, though, the feed problem and subsequent slamming into the feed ramp only happens with IMI 556. I tried Federal XM193 and had no issue. I find this perplexing.

I did some more sleuthing tonight after a frustrating range trip and it appears the feed ramps in the barrel extension are further out than the feed ramps on the Mega receiver. I changed upper receivers to a forged Sionics. Interestingly, the feed ramps on the Sionics receiver are further out than the barrel extension, though this would obviously seem like the better situation. In comparison, the BCM factory upper feed ramps between the receiver and barrel extension mate seamlessly.

I hope to get to the range early next week and test again to see if this change solves the problem.

NC

[LMT/556]

IMI's powder selection may have an effect here, slightly too fast or slow for your config with the short barrel and reduced port.