The Geissele Super Modular Rail MK4 M-LOK 13.5" handguard is a lightweight, free-floating AR-15 rail system engineered for shooters who demand both modularity and accuracy. Built by Geissele Automatics—a name trusted in precision AR platforms—this M-LOK handguard combines aggressive weight reduction with the rigidity needed to maintain zero and repeatability through field use and maintenance cycles. Whether you're setting up a competitive rifle, a hunting build, or a duty carbine, the MK4's modular slot layout lets you configure your rail to fit your exact needs.

What sets the MK4 apart is Geissele's 2.25" proprietary barrel nut, which increases surface contact between the rail and receiver. That extra bearing surface translates to a handguard that stays straight and true across the entire free-float length, directly supporting shot-to-shot consistency and zero retention—critical when you're dialing in a rifle and want confidence that it'll hold its setting. The rail itself is vented extensively to shed heat and weight without sacrificing strength, and it ships with the barrel nut included.

The M-LOK attachment points run across the 3, 6, and 9 o'clock sides, plus both upper 45-degree quadrants, giving you plenty of real estate to mount lights, grips, rail panels, or other accessories. Short integrated M1913 picatinny sections at the fore (3, 6, 9 o'clock) also provide flexibility for traditionalist setups or hybrid configurations. Installation requires a Geissele barrel nut wrench, sold separately.