A machined aluminum multi-rail handguard specifically designed for the Special Operations Command (SOCOM) M4A1 carbine, the RIS II enables installation of an M203 40mm grenade launcher, while allowing the barrel to free float. The M203 attaches to the bottom rail quickly and easily, without special tools or additional parts. Full-length, MIL-STD 1913 Picatinny rails provide plenty of space to add other mission-specific accessories as needed. Top rail is designed to mate continously with the receiver rail. All models come with all required mounting hardware, instructions, and three molded polymer, snap-on rail covers. RIS II requires the installation of a low-profile gas block. FSP RIS II models have a cutout in the top rail that allows retention of the standard A2 gas block/front sight tower on a carbine-length gas system. MK 18 RIS II is specifically designed for an M4A1 carbine with Mk18 CQBR (Close Quarters Battle Receiver) upper receiver and 10.3" barrel. Provides barrel free-float and expanded accessory mounting options, while deleting M203 mounting capability. Requires low-profile gas block.
AR-15, Issue:09, Page:041
Big Book Catalog, Issue:67, Page:044