FN USA FN 15 Military Collector Series M16A4 Complete Upper Receiver Assembly 5.56mm 20" Barrel

The FN USA FN 15 Military Collector Series M16A4 complete upper receiver assembly brings authentic military-pattern engineering to your 5.56mm build. This isn't a rebranded clone—FN manufactured these uppers to the same exacting standards that defined the M16's decades of service. If you're assembling an M16-style rifle or want period-correct components for a clone build, this upper delivers genuine mil-spec construction with documented heritage.

Built around a 20-inch chrome-lined barrel with a 1:7 right-hand twist, the upper handles 5.56x45mm NATO ammunition and feeds reliably with the included direct impingement, rifle-length gas system. The barrel is button-broached for consistent rifling, and the complete M16-style bolt carrier group features a Carpenter 158 steel bolt that's been HPT/MPI tested—the same verification process military armorers demand. This isn't surplus or reproduction in the loose sense; it's FN's official take on what that rifle looked like, built to the specs that worked.

The quad-rail setup pairs a Knight's Armament M5RAS system with matching adapter, giving you modern modularity while keeping the profile historically accurate. The A2-style front sight and adjustable rear sight round out a complete, ready-to-mount upper that works with any standard M16-pattern lower. For collectors, military history enthusiasts, and builders seeking authentic components rather than budget approximations, this upper is genuine FN craftsmanship.

Key Features

• FN-manufactured upper to original M16A4 military specifications
• 20-inch chrome-lined, button-broached barrel in 5.56x45mm NATO
• Complete mil-spec M16-style bolt carrier group with HPT/MPI-tested Carpenter 158 bolt
• Direct impingement, rifle-length gas system for reliable operation
• 1:7 right-hand twist for modern ammunition performance
• Knight's Armament M5RAS quad-rail with adapter for accessory mounting
• A2-style front and adjustable rear sights included

Specifications

Frequently Asked Questions

What lower receiver does this upper work with?

This is a standard M16-pattern upper and will mate with any M16-compatible lower receiver. It's designed for direct compatibility with traditional mil-spec lowers.

Is the bolt carrier group complete and ready to use?

Yes. The upper ships with a complete M16-style mil-spec bolt carrier group, including the HPT/MPI-tested Carpenter 158 bolt. You'll need to assemble it to a lower and add ammunition—the upper itself is ready to go.

What makes this a "collector series" upper?

FN built this upper as an authentic reproduction of the original M16A4, adhering to the same military and FN specifications. It's designed for shooters and collectors who want genuine mil-spec components rather than budget alternatives or rebranded imports.

Can I remove or swap out the sights and rails?

The A2-style front sight and adjustable rear sight are included. The Knight's Armament M5RAS quad-rail system is standard AR-pattern and allows mounting of modern optics and accessories, but those specifics are what ship with the upper.