Geissele MK4 Federal Rail

The Geissele MK4 Federal Rail is the same handguard used to fulfill contracts for the Federal Bureau of Investigation (FBI), representing Geissele's solution for agencies requiring integrated Picatinny sections at critical mounting locations combined with M-LOK modularity everywhere else. Machined from 7000 series aluminum with Type-3 hardcoat anodizing, the 10-inch MK4 weighs 10.2 ounces without the barrel nut and 11.8 ounces with it, offering a balanced approach between the weight of full quad rails and the minimalism of pure M-LOK systems.

The MK4 features integrated M1913 Picatinny rail sections at the fore of the rail in the 3, 6, and 9 o'clock positions, with the bottom 6 o'clock Picatinny rail elongated to more comfortably accommodate accessories like vertical grips and lights. M-LOK slots are positioned at the 3, 6, and 9 o'clock positions as well as the upper 45-degree quadrants, providing ample mounting options for modern accessories. The full-length Picatinny top rail accommodates optics, backup sights, and laser aiming devices without requiring additional rail sections.

Designed specifically to work with mil-spec M4 upper receivers, the MK4 provides the rigidity and durability expected from Geissele while delivering the mounting versatility that federal agencies demanded. The combination of integrated Picatinny at key positions with M-LOK elsewhere gives users the best of both worlds: rock-solid accessory mounting where it matters most, with weight savings and adaptability everywhere else. The MK4's adoption by the FBI validates its design for professional law enforcement and serious civilian applications where reliability and versatility cannot be compromised.