The Geissele Super Modular Rail MK4, sold here in a 13.5-inch length (brand part no. 05-278S), is Geissele Automatics’ ultra-lightweight M-LOK handguard built for shooters who want a purpose-built free-float rail without excess weight. It features integrated short M1913 picatinny rail sections at the 3, 6, and 9 o’clock positions near the front of the rail, along with M-LOK slots at those same positions and across the upper 45-degree quadrants for full accessory modularity. Maximum venting cuts weight and dramatically improves heat dissipation. The SMR MK4 also uses Geissele’s proprietary 2.25-inch-long barrel nut, which increases the contact surface between the rail and receiver so the platform stays straight and true, improving accuracy and zero repeatability through disassembly and reassembly. It requires a Geissele barrel nut wrench for installation, sold separately.

Key Specifications

• Measures 13.5 inches in length, sized for a mid-length or rifle-length gas system build.
• Uses M-LOK accessory slots at the 3, 6, and 9 o’clock positions plus the upper 45-degree quadrants.
• Includes integrated short M1913 picatinny rail sections at the front for sights or accessories.
• Maximum venting cuts weight and provides heat dissipation during sustained fire.
• Uses a proprietary 2.25-inch barrel nut for a straight, true, and zero-repeatable mounting surface.

Frequently Asked Questions

What mounting system does this handguard use? M-LOK, with short M1913 picatinny sections up front.

How long is this handguard? 13.5 inches.

Do I need a special tool to install it? Yes, a Geissele barrel nut wrench, sold separately, is required.

Buy the Geissele Super Modular Rail MK4 M-LOK Handguard, 13.5-Inch

Order the Geissele SMR MK4 handguard from Geissele Automatics through our AR-15 handguards lineup. It ships fast from our Lubbock, Texas gun shop, fully insured.