Knights Armament M4 RAS Forend Assembly - Black Tactical Rail System

The Knights Armament M4 RAS (Rail Adapter System) is a field-proven quad-rail forend assembly built on the same design that has equipped over a million military M4 Carbines. If you're running a standard AR-15 with a carbine-length gas system and want to upgrade from a basic polymer handguard to a modular, Picatinny-railed platform, the M4 RAS is a drop-in replacement that locks down solid and gives you real real estate for mounting optics, lights, lasers, and other tactical accessories along the full length of the forend.

What makes the KAC M4 RAS stand out among quad-rail options is its barrel nut clamp-and-screw locking mechanism. Rather than relying on the fit of the handguard alone, this design anchors the rail directly to your rifle's barrel nut, creating a rigid, stable platform that won't shift under recoil or the weight of mounted gear. That kind of rock-solid mounting matters whether you're building a duty carbine, a tactical rifle, or a precision AR that demands accessory placement you can count on. The rail is furnished with three KAC 11 Rib Rail Panels to cover the quad slots, keeping your hands protected from sharp edges and reducing snag points in the field.

Installation is straightforward—it's designed as a drop-in replacement for the original two-piece polymer M4-type handguard on rifles with a delta ring assembly and fixed front sight/gas block. Lighter barrel profiles (M4 or Government contours) fit without modification; heavier profiles may require some fitting work. The M4 RAS is built for AR-15 and SR-15 platforms only and is not compatible with SR-25 variants. Installation instructions are included with the assembly.

Key Features

• Full-length Mil-Spec M1913 Picatinny rails on all four sides for unrestricted accessory mounting
• Barrel nut clamp-and-screw locking system delivers zero play and superior stability
• Drop-in replacement for standard M4-type polymer handguards on carbine-length AR platforms
• Includes three KAC 11 Rib Rail Panels for hand protection and thermal management
• Battle-tested design with over 1 million units in military service
• Non-free float configuration; compatible with fixed front sight and delta ring assemblies

Specifications

Frequently Asked Questions

What AR-15s will the M4 RAS fit?

The M4 RAS is a drop-in replacement for AR-15 and SR-15 rifles with a carbine-length gas system, delta ring assembly, fixed front sight/gas block, and round handguard end cap. Your rifle must have a standard two-piece polymer M4-type handguard to replace. It is not compatible with free-float systems or SR-25 platforms.

Does barrel contour matter?

Yes. Lighter barrel profiles such as M4 or Government contours fit without modification. If your rifle has a heavier barrel contour, the inside of the rail may require modification to accommodate it properly.

What accessories can I mount on the quad rails?

The M4 RAS features full-length Mil-Spec M1913 Picatinny rails on all four sides, so any standard Picatinny-mount accessory—optics, lights, lasers, vertical grips, slings, and other tactical gear—can be mounted anywhere along the length of the forend.

What's included in the box?

The M4 RAS forend assembly ships with three KAC 11 Rib Rail Panels to cover the quad slots, protecting your hands and reducing snag points. Installation instructions are also included.