In 1966 I was told to go get my sniper rifle. So being a 101st NCO and the Armorer for the rifle team, it was yes sir. I called Div supply got any Remington 700s, no, how about Win 70s no, have you got anything that will shoot over 300, yes, the M-14s you guys traded in, last year. So I go get a requisition for 14 M-14s for aggressor force use. I take my Jeep to supply and hand pick 14 likely candidates. Hey you guys have a scope mount for at lest one, yep seems like we have one in a box somewhere around here, that in the Airborne means your damed straight we do. Got a scope, nope. I bought my own 3-9 Redfield out of my pocket. Made my own sniper rifle. It was OK for what it was.
Fast forward 30 years, I bought an Armalite AR-10T then built an upper in 260 with a Lilja SS, 1-8 barrel 20” long with a free float handguard and an adjustable gas block. In 1966 I would have given a left nut for that 260. I put 3 rounds, rapid fire, Into the left eye socket of a life size face picture target at 500 meters. In front of 3 witnesses.
I no longer own any M-14 or M1A rifles and have not done so since I met the 260 AR-10. Basicly it is a laser and if you can see it you can hit it.
Oh, the light weight 308 AR is a RRA LAR with barrels that only fit it. Look up the 308 AR site, it has perhaps 30 pages on 308 ARs and what is and is not an AR-10 the Armalite is the one and only AR-10, unless made under license but still to AR-10 specs for strength and fit.