After trying every combination of light / mount for my second ACR (soon to be a 10.5" 5.56 / 11.5" 300BLK) I decided to work up a better solution. A few loose measurements, some drilling, and two screws later I came up with this. I mounted the light directly to the starboard forward rail. It pulled the light in tighter. It also allowed me to use a SR07 tape switch at 12 o'clock.

This will only work with the enhanced handguard. It solves a lot of problems for me and saves a little weight. You could also mount it on the port side with a push button tailcap.

The good thing about this mod is that it is simple and quick. I coated the bare aluminum with gunkote and loctited the screws (6-32 by the way).

It also allowed me to move the AFG forward two slots and get my thumb on the top rail.

Sorry for the poor pictures.