Had good luck with a Nikon on my M1A. I currently use a Buckmaster with mil-dot. The Monarch Mils are super nice, and affordable. If you want to go with rugged, and slightly better quality, but don't want to break the bank, the Trijicon Accupoints are tremendous scopes for the money.
The .308 isn't really a strong 1000 yard round. Even the Army refers to it as 800 yard effective range. Couple that to a shorter, non-match grade barrel, and you'll have your work cut out for you. Be sure to stock up on match grade ammunition. Something heavier and stable for the flight. Had great luck with Black Hills Match w/ 155 grain A-Max bullet. Not out to that distance, but shoots between 1/2 and 3/4 moa at 100, very reliable to 350. Farthest I've shot it so far, but would definitely trust it to 600. Best of luck.