AR10 feeding issue

[PrimoLuvr]

I recently purchased a 'used' Aero AR10, built by Compass Lake. Looking at the barrel through the borescope leads me to believe the gun was only fired by CLE after assembly. The rifle was built in 2019, 1 of 3 for a single customer. The rifle is a joy to shoot. I've only 82 rounds through it, just starting load development. The basic specs are:
Aero enhanced upper
Aero lower
Aero black nitride BCG
20" Kreiger 10-twist barrel, .875" gas block journal
M118LR chamber
Adj gas block (I installed this)
PRS stock
VG6 Gamma muzzle brake (I installed this)
Geissele NM trigger, with light match springs

I've acquired 3 new LaRue magazines for the rifle but am having an issue with all of them. The 2nd to last round will not feed from the magazine, the bolt normally skips over the top of it or pushes it forward 3/4" then jumps over the case rim and jams into the body.

Is there a standard for the magazine feed lip spread or how much of the magazine should extend above the lower receiver?

I'm shooting reloads with COAL of 2.800". The feeding issue happens while; shooting from a loaded magazine, loading 2 rounds in the magazines and pulling back the charging handle or releasing the bolt, or slowly closing the action with the charging handle. Any guidance on determining root cause will be GREATLY appreciated.

 

[Jgault]

I have a few 308 ar’s, what I’ve found is mine and everyone I’ve dealt with with the exception of a few are picky little bitches. One of mine will use any magazine but half won’t drop free, the other will work fine with a 15 round magpul but has the same problem your having with 25 round magpul, but it runs any steel magazine just fine. I did find that this particular issue is more bolt specific than rifle specific, I have changed the bolts and some bolts just function fine but another bolt won’t function well with certain magazine brand and rifle combination. I don’t believe there is anything inherently wrong with the rifle.

 

[bfoosh006]

For the OP, I can't help but wonder if your mag catch is wonky... next time your try to test the feeding... see if you can push the bottom of the LaRue upward and if that makes a difference. Myself, I would install a mag catch that more thoroughly / fully engages the mag catch button.

I would try and check if snugging up or loosening the mag catch helps as well.

I would also try some Magpul mags ...

Lots of times magcatches can be just "off" enough to "mess" with mags feeding.

Jgault.... for the lower that won't drop free mags. try burnishing the interior of the magwell, with gun oil and Quad Ought Steelwool... ( 0000 )
Sometimes it needs a little smoothing up.

 

[Cascade Hemi]

For the OP, I can't help but wonder if your mag catch is wonky... next time your try to test the feeding... see if you can push the bottom of the LaRue upward and if that makes a difference. Myself, I would install a mag catch that more thoroughly / fully engages the mag catch button.

I would try and check if snugging up or loosening the mag catch helps as well.

I would also try some Magpul mags ...

Lots of times magcatches can be just "off" enough to "mess" with mags feeding.

Jgault.... for the lower that won't drop free mags. try burnishing the interior of the magwell, with gun oil and Quad Ought Steelwool... ( 0000 )
Sometimes it needs a little smoothing up.

OP has an Aero M5 lower parts kit because the M5 lower has some proprietary parts. It uses an extended button specifically for the M5 lower. The mag catch does not thread all the way into the button like a traditional AR15 or other LFAR lowers. The M5 does, however, take standard AR15 catches instead of DPMS pattern catches.

 

[PrimoLuvr]

I put a magazine in the rifle with a couple empty casings, like pictured above. When slowly closing the bolt there's definitely less than .010" of contact with the case rim on the right side, 2nd from empty. When doing the same with the last round in the mag there's more than double that.

I think I'll order some sample mags from ASC and Duramag, these appear to allow the longest COAL. In the meantime I may try and tweak the feed lips on the Larue mags.

 

[PrimoLuvr]

For the OP, I can't help but wonder if your mag catch is wonky... next time your try to test the feeding... see if you can push the bottom of the LaRue upward and if that makes a difference. Myself, I would install a mag catch that more thoroughly / fully engages the mag catch button.

I would try and check if snugging up or loosening the mag catch helps as well.

I would also try some Magpul mags ...

Lots of times magcatches can be just "off" enough to "mess" with mags feeding.

Jgault.... for the lower that won't drop free mags. try burnishing the interior of the magwell, with gun oil and Quad Ought Steelwool... ( 0000 )
Sometimes it needs a little smoothing up.

With the magazine inserted there's roughly an additional .010-.015" that I can push it upward before the mag catch bottoms out in the slot.

Tightening/loosening the mag catch hasn't made a difference as it already positively locks in the mag slot. The mag catch is flush with the top of the hole in the frame, it can't move up any highter.

 

[Cascade Hemi]

I put a magazine in the rifle with a couple empty casings, like pictured above. When slowly closing the bolt there's definitely less than .010" of contact with the case rim on the right side, 2nd from empty. When doing the same with the last round in the mag there's more than double that.

I think I'll order some sample mags from ASC and Duramag, these appear to allow the longest COAL. In the meantime I may try and tweak the feed lips on the Larue mags.

Lancer mags are almost universally the answer.

 

[PrimoLuvr]

Lancer mags are almost universally the answer.

Is the max COAL with Lancer 2.84"?

 

[Cascade Hemi]

Is the max COAL with Lancer 2.84"?

Yes

 

[PrimoLuvr]

I received 2 ASC and 2 Duramag magazines. The Duramags position the rounds much higher so there's .020-.030" of contact between the bolt lug and the case rim. Hopefully these will function fine. The ASC mags don't allow an empty case to sit flush against the feed lips, these will never feed a round so they're being returned.
I called Larue about their magazines and they said their M110 pattern lower is different than my AR10 pattern Aero lower. Will the differences actually affect magazines?

 

[PrimoLuvr]

The Mag Shack returned the ASC magazines and replaced them with Duramags. I tested out 4 Duramag magazines yesterday and the rifle functioned without any issues now.

 

[padom]

Ive built 50+ large from gassers and only 1 I had a mag feeding issue. ALL my builds use KAC SR25 mags (cream of the crop) and ASC SS SR25 mags.

The 1 build that had a mag issue was an AERO M5 lower. Up until that point, I used a lot of AERO AR15 receivers without issue (this was many years ago). Ended up the M5 lower was mis machined, confirmed by AERO after sending it in. Their CS was the worlds worst to deal with, took 5 months to get a replacement with being told over and over it shipped, then being told an employee handling my RMA was fired and his paperwork was a mess.

I finally got the new M5 lower, confirmed it worked and sold it. Didnt even build off it. Never bought or used an AERO part ever again after that dumpster fire.

Not saying there is anything wrong with your M5 Lower. But I am saying there could be and needs to be checked. Order an ASC SR25 mag and check. KAC SR25 mags are the best but super expensive.

SR-25 AR10 .308 | 10 Rd Stainless Steel Magazine

Our 10rd .308 magazines meet the highest standards. When you buy our magazines, you're investing in guaranteed toughness, and reliability. Shop ASC .308 magazines today!

www.ammosc.com

SR-25 AR10 .308 | 20 Rd Stainless Steel Magazine

Our 20rd .308 magazines meet the highest standards. When you buy our magazines, you're investing in guaranteed toughness, and reliability. Shop ASC .308 magazines today!

www.ammosc.com

 

[PrimoLuvr]

Ive built 50+ large from gassers and only 1 I had a mag feeding issue. ALL my builds use KAC SR25 mags (cream of the crop) and ASC SS SR25 mags.

The 1 build that had a mag issue was an AERO M5 lower. Up until that point, I used a lot of AERO AR15 receivers without issue (this was many years ago). Ended up the M5 lower was mis machined, confirmed by AERO after sending it in. Their CS was the worlds worst to deal with, took 5 months to get a replacement with being told over and over it shipped, then being told an employee handling my RMA was fired and his paperwork was a mess.

I finally got the new M5 lower, confirmed it worked and sold it. Didnt even build off it. Never bought or used an AERO part ever again after that dumpster fire.

Not saying there is anything wrong with your M5 Lower. But I am saying there could be and needs to be checked. Order an ASC SR25 mag and check. KAC SR25 mags are the best but super expensive.

SR-25 AR10 .308 | 10 Rd Stainless Steel Magazine

Our 10rd .308 magazines meet the highest standards. When you buy our magazines, you're investing in guaranteed toughness, and reliability. Shop ASC .308 magazines today!

www.ammosc.com

SR-25 AR10 .308 | 20 Rd Stainless Steel Magazine

Our 20rd .308 magazines meet the highest standards. When you buy our magazines, you're investing in guaranteed toughness, and reliability. Shop ASC .308 magazines today!

www.ammosc.com

Thank you for the reply.
I did order a couple ASC SR25 magazines but the cartridges didn't sit flush against the lips, the casehead was gapping about .020". I looked around and couldn't find any KAC magazines anywhere. I put another 50 rounds through the rifle today without issue using the Duramag magazines.