AR Feed Issues

[patio]

I have been trouble shooting feed issues on my SBR over the past few weeks. I took my Noveske 10.5" CQB 5.56mm upper to the range inserted a 30 round magazine, released the bolt, pulled the trigger, BANG. The next round to feed got hung up on the feed ramps. I dropped the magazine and the round fed. But the cycle of every other round not feeding continued even when using half a dozen other magazines.

So this morning I grabbed an extra BCG and a magazine to see if I could duplicate/troubleshooet. As expected the second round would not feed, but I touched the magazine while trying to get a better look at the hang up and it moved enough to feed the round. Continuing on I had 4 out of 30 rounds hang, all were unhung by just jiggling the magazine.

This is frustrating me because I have had no issues with another uppers I have put on this lower.

So is it the BCG? The feed ramps? The magazines? The buffer spring? Any ideas would be greatly appreciated.

 

[vellnueve]

Sounds like a feedramp problem for sure.

 

[patio]

Sounds like a feedramp problem for sure.

Gah, not what I wanted to hear. I have a note into Noveske but haven't heard anything back.

 

[MassMark]

Sounds like a feedramp problem for sure.

Not necessarily...First, what are you running for BCG's? Second, what are you running for a buffer? Third, what is the status of your magazine release? Fourth, what are you running for ammo? Fifth, check your gas system. Sixth, pull your upper and inspect your feed ramps. I suspect that it's your buffer and/or your spring. If you're running a SA BCG, that could be it as well. Magazine lock-up and the geometry of your upper may be at issue as well....

 

[vellnueve]

Well, it sounds like all his other uppers function fine on the same setup, so I'd eliminate magazine lock-up issues.

 

[patio]

Not necessarily...First, what are you running for BCG's?

I tried it with the BCG that came with the Noveske upper as well as the BCG that came with a Model 1 upper. Both are new, under 10 rounds on both.

Second, what are you running for a buffer?

The spring and buffer are the original from the lower, which are SA.

Third, what is the status of your magazine release?

Not sure what you mean.

Fourth, what are you running for ammo?

I tried Federal XM, some Argentine stuff FS had a while back and some Privi.

Fifth, check your gas system.

Haven't will tonight/tomorrow and report back.

Sixth, pull your upper and inspect your feed ramps.

I did, they look good. Clinotus looked them over too. I will grab a few shots of a hung round tonight/tomorrow.

I suspect that it's your buffer and/or your spring. If you're running a SA BCG, that could be it as well. Magazine lock-up and the geometry of your upper may be at issue as well....

OK, lets assume its the buffer/spring. What would you suggest I run? I knew when I rebuilt it I should have done a tad more research since I knew springs/buffers on SBRs were sometimes finicky.

Will report back. Any other ideas to check while I have it apart are welcomed.

 

[Make It In Mass]

Is the bolt hanging up on the rear corner of the magazine? You mention that moving the magazine will cause it to come loose and feed.

When feeding every other round, is the round that hangs up always on the right side of the magazine, closest to the ejection port?

Do you use these magazines in any other AR's ? How do they perform?

Is your SBR built from parts or purchased as a finished firearm?

When was the last time you thoroughly cleaned the magazines?

Next time at the range, try pushing forward on the magazine a bit (pointing the cartridge nose up) when you fire. Does this improve the feeding situation?

I had a situation that sounds very similar to yours. After about 1,000 rounds through four "working" 30-round magazines, one day the carbine stopped feeding properly from the right-hand stack, and rounds were jamming on the feed ramps. All magazines acted the same. I pushed forward gently on the magazine while firing and feeding greatly improved. I substituted the seldom-used 10-round magazine and it worked perfectly.

Now it gets interesting. The cartridge height in the 30-round magazines, defined by how far the bullet tip rises above the edge of the magazine, was visibly less than the 10-round magazine. It seemed that the feed lips were mildly compressed, holding the cartridge lower in the magazine. As the bottleneck section of the cartridge would ride over the edge of the magazine, it would jump up, then down, hanging on the feedramps (my theory, as you would need a high-speed camera to verify this).

Contrary to good trouble-shooting practices, I did two corrective actions at once. I cleaned the magazines with a specially-designed AR-15 mag brush (they were visibly sooty on the inside and the followers made more noise than usual when depressed. Then I gently adjusted the feedlips with a specially designed tool (don't do this with pliers) so the bullet tips were riding at the same height as in my 10-round magazine. I use .223 snap-caps as a "standard" so no live ammunition, with its variances, is used to do this.

The next trip to the range, all was running smoothly again. My conclusion is that dirty mags slowed the feeding speed and after ejection of the spent cartridge with the bolt lugs pushing the next cartridge down in the magazine, it doesn't rebound fully and is stripped while low in the magazine, causing it to jump over the magazine edge.

Feeding issues are largely caused by magazine problems and timing issues play more of a role than most people realize.

 

[MassMark]

Well, it sounds like all his other uppers function fine on the same setup, so I'd eliminate magazine lock-up issues.

Again - not necessarily. "Spec" is somewhat a broad term and the variances from manufacturer to manufacturer could indeed be wreaking havoc.If the mag is not seating properly, it may indeed be functional on one upper and not on another. I would still suspect that this is not a ramp issue, but is rather closely connected to the buffer, spring and/or bolt carrier group. A short rifle - especially an SBR depends on the right set up. A heavy, or H buffer should be used long with an M-16, rather than an AR-15 bolt carrier group...