Streamlight Protac Rail Mount HL-X. 1000 lumens, nice and sturdy, compatible with Arisaka and other Surefire scout light mounts. Can be had for about $105-120 on Amazon depending if you want all the accessories or just the barebones package with a pushbutton tail cap only. Only real downside is the tape switch is integrated with the tail cap which makes it kinda tough to remove the cap to change the battery if you've got the wire zip-tied to the rail.