This is a Burris Ring known as the Xtreme Tactical, model 420163.
Xtreme Tactical Rings were built to withstand brutal use from competitors and tactical operators. They are lightweight" have plenty of holding power" and can endure any amount of recoil.
Features:
Fits on any weaver or picatinny-style mount
Ideal for tactical use
Great for hunting rifles slug guns' and muzzleloaders