They've been discontinued, but I'm partial to the Nikon Force XR variable. If you happen find one for sale, even if it's used, it's well worth it in my opinion.

I don't think the Blackout will truly warrant it, but go with a steel base and steel scope rings, not aluminum. Our handguns are much harder on scope mounts than rifles, and several members here have had issues with their mounting systems. MGM's steel bases are rock solid, as are Warne bases and rings. Again, the Blackout might not recoil enough to cause problems, but it never hurts to have insurance. If you ever do a 460 build, it definitely will require steel mounts, along with 3 or 4 scope rings.