If you need it, you need it - JP Enterprises Tactical Rail Kit Accessories

If you have a JP MkIII handguard, and you want to mount something that needs this much rail space, well, you need this. Nicely sized for a Magpul AFG2.

Well made, of course. Silly expensive. Perhaps a tad heavy if you're counting every ounce.

A tip: included are 3 10-32 screws and a threaded backer plate with 3 holes. Note that there is a 10-32 threaded hole in the fore/aft center of the handguard in the 6 o'clock position. You can put one of the screws in that hole instead of the backer plate and it works fine, so your position options along the bottom of the handguard are basically unlimited.