AAC BCG issue, need some input

FoxAlpha

FoxAlpha

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So I was finally able to take my recent builds to the range this past weekend, encountered an issue with my AAC BCG or so I presume that's the issue. Tried googling the issue but couldn't find someone who has my simalir issue

Specs:
Spikes upper
DD 10.3 Barrel
AAC NIB BCG
Assembled by Greg at Tier one armory who also had checked the headspace and said it was good to go.

Anyways, fired off a few rounds and every 2nd or 3rd round the BCG would strip a round from the mag, and as the bolt lugs were entering the barrel extension it would bind and lock up. Bolt would not go into battery where id meet a dead trigger. Forward assist would not push it forward, and when I tried to rack the bolt with the charging handle it was seized in and I'd have to mortar it on the bench to clear it. Happened every time I tried it with the AAC BCG. I swapped my LMT BCG into the SBR upper and it ran flawlessly, so I tried the AAC BCG in my 16" BCM upper and it had the exact same issue every 2-3 rounds.
Happened on all types of mags, PMAG, Beowulf, USGI, hence my hypothesis that it's an issue with the bolt carrier.
Only thing I noticed with the AAC is 2 of the gas ring "holes" we're lined up when I pulled the bolt apart but this was after we had left the range.
I should have swapped just the bolts in the different carriers but hadn't thought of this until the evening.

If it helps, both uppers were run off the same lower with an H buffer in the tube using American eagle 223 and some PMC 556.

Need some help on this from the experts.
 
An AR can cycle perfectly fine without any issues with the gas ring gaps being aligned.

Does the bolt get hung up if you manually cycle it without any ammo?

If the bolt is binding on two different uppers, sure sounds like it's something to do with the bolt.
 
For lube, I've always used Lucas red n tacky #2 on all of my AR's with good success. After the first initial problems I cleaned it off and gave it a pretty heavy helping of gun oil.

I do have some dummy rounds, I'll be giving it a try this evening.
 
The "worn gas tube" like above doesn't affect functionality. It is just a bit annoying the BCG slides out whenever the upper cracks open. That is it.
 
It's not a gas tube issue, it wouldn't explain why the bolt is getting seized as it passes through the lugs in the barrel extension on its way into the chamber.

FWIW, both gas tubes on both uppers are either brand new, or practically new. No wear like the one pictures above.
I'm going to try and drop in to CSC next weekend and try trouble shooting some more.
 
rdavidson said:
My guess is gas tube and gas key.
Click to expand...

If you're suggesting the gas key is getting hung up on a misaligned gas tube, I've checked that already. Took the bolt out of the carrier and watched the gas key capture the gas tube with proper alignment each time, again on both uppers.
 
Before I bought my nib bcg I was reading people have issues with nib coating in gas key the gas tube would not go in all the way to gas key causing the bcg not to go in to full battery.
Was happening to then every few rounds.
This was happening with reputable bcg, but the nib coating is only done by 1 or 2 company's.
They had to use a different gas tube.
Some had to clean up inside of gas key because of coating.
 
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