FAB Defense FXRBS Rear Back-Up Sight – Dual Aperture

The FAB Defense FXRBS is an auxiliary rear sight designed for shooters who want a reliable backup or primary sighting option on their AR-15, M16, or M4 rifle. It pairs with any front sight and is engineered to give an extreme optical advantage whether you're running it as your main sight or holding it in reserve behind an optic.

This sight mounts directly to any 1913 Picatinny rail, making installation quick on nearly any modern AR-platform rifle. The angel-wing-shaped front shroud helps center the sight picture with your front sight, while the low folded profile stays smooth and out of the way so it won't snag on gear, slings, or brush. Deployment is instant thanks to a spring-locked mechanism that snaps into position without slipping, breaking, or deforming. The housing is built from a combination of high-grade polymer and metal for long-term durability.

Key Specifications

• Aperture Sizes: 3mm and 1.5mm dual apertures
• 3mm Aperture: Longer eye relief, low light use, faster target acquisition
• 1.5mm Aperture: Shorter eye relief mounting for greater precision
• Mounting: Fits any standard 1913 Picatinny rail
• Profile: Low folded profile for a snag-free carry
• Deployment: Spring-locked, instant deployment mechanism
• Construction: High-grade polymer and metal housing
• Front Shroud: Angel-wing shape for centering sight picture with any front sight
• Compatibility: AR-15, M16, and M4 platforms
• Weight: 1.8 ounces

Whether you need a dependable backup behind a red dot or LPVO, or a standalone rear sight for your AR-platform rifle, the FAB Defense FXRBS for sale at Loftus Firearms delivers fast, durable performance you can count on.