Geissele Mk4 Federal 10" ODG Rail for FBI build

The Geissele Super Modular Rail (SMR) Mk4 Federal in 10-inch length and OD Green is the correct handguard for any FBI HRT clone build or federal law enforcement-pattern AR pistol or SBR. This is the rail Geissele manufactured under contract for the Federal Bureau of Investigation — the same part, in the same OD Green Cerakote, that appears on issued FBI rifles.

The "Federal" designation refers to the Mod 2 profile with the extended lower-rail Picatinny section — longer than the standard Mk4 SMR — to support FBI-specified foregrip, light, and pressure-switch placement. The rest of the geometry is pure Geissele: M-LOK slots on the three non-rail sides, a proprietary barrel nut interface that torque-indexes reliably, and an aluminum extrusion that shrugs off hard use.

The Mk4 SMR was one of the first free-float M-LOK rails on the market and remains one of the most respected. It is a go-to choice for AR pistols, short-barreled rifles, and PDW builds where weight, rigidity, and mounting real estate all matter. The 10-inch length pairs perfectly with 10.3" and 11.5" barrels for FBI HRT and Federal LE clone configurations.

Authentic, correct, and ready to build. Order yours today.