If you don't want to use any mount, or drill and tap, Aimpoint makes a high quality Red dot that mounts directly on any vent rib right out of the box. It is the Aimpoint Micro- S. A bit pricey, but mounts low right on the rib. The Army uses Aimpoint. Reliable, battery lasts forever, and has a lot of brightness adjustment. Has a 6 MOA size Red dot. I love mine. You can put it on any rib. Very well made.....good luck....