Fab Defense M4 Picatinny Under Rail for AR-15/M4/M16 Handguards Black

The Fab Defense M4 Picatinny Under Rail for AR-15/M4/M16 Handguards in black is a modular accessory mounting solution designed for operators who need flexible rail real estate without adding bulk to their carbine's forend. Built for law enforcement, military, and civilian tactical shooters, this under-rail system addresses a critical gap: mounting bipods, vertical grips, cable cutters, or other mission-critical gear directly below the handguard where they remain accessible and co-witness with your primary optic.

F.A.B. Defense engineered this rail to integrate seamlessly with standard AR handguards, providing reliable Picatinny interface geometry without requiring permanent modifications to your weapon system. This under-rail features precision-machined aluminum construction with a hardcoat anodized black finish that resists corrosion and wear in field environments. The Picatinny standardization ensures compatibility with any MIL-STD-1913 accessory—whether that's a Harris bipod, rail-mounted forward grip, or dedicated light bracket.

At just 0.20 lbs, the minimal weight penalty makes it practical for extended patrol or tactical operations where every ounce matters. The compact 4.8-inch profile fits most handguard lengths without extending into the magwell, preserving natural grip ergonomics and reload speed. Installation is tool-free on most quad-rail and Picatinny handguard systems, allowing rapid mounting or removal in the field.