I put these on my last two 308's, i really like them and they don't cost a fortune. I hunt with my AR's mostly.
Leapers, Inc. - Hunting/Shooting, Sporting Goods and Security Gear
The Ruger SR 7.62 is piston drive as is the Adams Arms rifle. AA is a fishy company id stay away from. The Ruger is a heavy beast and seems well made although mines not that accurate for some reason. just haven't used the right ammo yet. My AA jams often. Not a lot of offerings of pistons in the 308.