Sounds like a tight chamber. If it's not - NOT - an Armalite, then it's NOT an AR-10.
Not OUR call, that's ARMALITE's call. Get that straight, and it's NOT on us.
Start a tech thread in the appropriate section on this...
Welcome.
Nope.
That's the 5/8" spacer used to run the A2 stock (with its longer vented screw). It's not used to make the stock longer - it's used to make the rifle receiver extension fit the longer A2 stock.
Can't say how much I really like this trigger - unreal for a $99 trigger, when on sale, or even a $125 trigger when it's NOT on sale. It's a damn good 2-stage trigger.
Yep, looks to be straight-DPMS based now, including receiver cut. The integrated trigger guard changed in shape/design, too.
That upper receiver rail still is the same, though - needs another cut in it, at the back.
On that same note of Matrix Aerospace receiver sets... Live Free Armory is using a different design now that they are branded as their own sets. Not the exact same as the old Matrix sets anymore. See this link for visual detail dfferences:
http://www.livefreearmory.com/product/matrix-aerospace-m-762-receiver-set-15-key-mod-hand-guard-and-lower-parts-kit-cerakoted-fde/
Aaaaah, AAC, as well. From the above,if money was no object, I'd personally buy the Noveske barrel. If I couldn't swing the Noveske, it would definitely be Ballistic Advantage (and they are a Site Sponsor here, brother).
Noveske, Bison Armory, Ballistic Advantage, PSA, KAK. Not many choices for that length. TONS of choices for 7.5", if he decides to go that route, over 8.5".
Degrease it, and you can run M-Pro 7 in the meantime, and I'll get you hooked up with The Lube...
I'll get you some pics of where the carrier wears the most - get the lube there, for sure.