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  • Post last modified:October 26, 2023

Here is how to build a M16A4 clone using these parts. The core features of of the M16A4 is a smooth shooting performance that features a rifle-length gas system on a 20 inch barrel configuration.

Here are 9 options to build a M16A4 semi-auto clone (also includes complete rifles).

M16A4 Clone Parts [Upper & Lower]

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PSA M16A4 Retro Lower Receiver 

psa ar15 retro lower

Palmetto State Armory can directly source Harrington Richardson receiver to build the most authentic M16A4 lower (Part 16471997). The receiver features retro markings like : "Property of US GOVT M16A4 5.56mm" to bring 

Aero Precision M16A4 Receiver

Aero precision M16A4 lower receiver

Aero Precision's special edition M16A4 lower receiver (APAR148017C)

features special retro markings including safe, semi, and burst selector markings (No third hole). The marking itself is not a perfect clone of the original but it would make a cool (and affordable) addition to any AR15 collection.

FN15 20" Barrel Complete Upper Receiver


If you want the most original M16A4 build from an official US Military contractor. The FNH USA FN15/AR upper receiver assemblies is for you! -

This FN complete upper assembly is the same one used on all military M16s, but marketed for civilian purchase. 

20" Barrel: Cold Hammer Forged Proprietary CrMoV Barrel Steel . Hard-Chrome Lined to MIL-STD 171. M4 Feed Ramps. High Pressure Tested. Magnetic Particle Inspected (MPI). Manganese Phosphate Finish. Chambered in 5.56X45mm. 1:7 RH Twist. 

Bolt Carrier Group: M16/Auto Bolt Carrier Assembly . Carpenter 158 Bolt. Bolt is Magnetic Particle Inspected (MPI). Staked Gas Key.

Colt R0901 

This is another name brand rifle gas length M16 upper from COLT. Colt parts are rare these days, and this is the same M16 Upper Receiver used on military's M16A2 and M16A4 rifles.

Government profile heavy barrel and feature a chrome lined bore and chamber, along with a 1-7 twist. The upper comes with Magpul MOE handguard.

PSA Rifle Length 20" Barrel + 15" M LOK Rail Full Kit

psa m16a4 build upper

PSA Part 5165493723

This is a perfect starter build kit to get to build a M16A4 clone. The kit includes a assembled upper featuring a rifle gas system and a 20" barrel already torqued and ready to go. All lower receiver parts are included without the serialized lower receiver.

Get a lower receiver like the ones and follow the lower receiver assembly guide to finish your M16A4 build. 

Barrel: 20" 416R stainless steel barrel, chambered in 5.56 NATO, with a 1:7 twist, M4 barrel extension, and a rifle-length gas system. The barrel is finished with a .750" diameter low-profile gas block

Upper: USA made Forged 7075-T6 A3 AR upper is hard coat anodized black for durability. Featuring M4 feed ramp cuts, andthe  PSA 15" Lightweight M-Lok Free Float Rail and an A2 flash hider.

Bolt Carrier Group: The Bolt is made of shot-peened, Mil-spec Carpenter 158® steel. Gas key is secured with grade 8 fasteners and staked.  Includes Charging Handle.

Lower Build Kit minus lower receiver:  PSA MOE EPT Lower Build Kit, Black

PSA BLEM 20" Rifle Length Gas System - Classic M16 Build + Lower Parts

PSA BLEM m16a4 full build kit minus lower

This is a classic complete M16 upper receiver without the modern bells and whistles. The upper features the classic delta A2 style front sight, rifle length gas system and polymer handguard.

The A2 profile barrel is Mil-Spec phosphate coated, High Pressure and Magnetic Particle inspected. 

FN CHF Barrel:  PSA sources FN barrel to finish this retro M16 rifle length build. The Machine Gun Steel grade barrel that is cold hammer forged to make it more durable.  The chrome process for the bore allows for a lining almost twice as thick as a standard M16 for enhanced durability.  Chambered in 5.56 NATO, with a 1:7 twist rate, M4 barrel extension, and a rifle length gas system.  

Upper: Forged 7075-T6 A3 AR upper is hard coat anodized black for durability. Featuring T-marks, these upper upper receivers are made for us right here in the USA.

BCG: The bolt is made of Mil-s\Spec shot-peened Carpenter 158 steel. Gas key is secured with grade 8 fasteners and staked per mil-spec. Bolt carrier is parkerized outside, and chrome lined inside.

PSA 20" A2 M16 Upper With Carrying Handle - No BCG

m16 a2 upper

This Mil Spec full gas length M16 upper is similar to the one recommended above and it ships from PSA with a A2 detachable carrying handle and it comes WITHOUT a BCG to save you some money if you already have some spare BCG parts laying around at home.

The barrel is 20" 4150V Chrome Moly vanadium steel, chambered in 5.56 NATO, with a 1:7 twist rate, M4 barrel extension, and a rifle length gas system. The A2-style profile barrel is nitride finished for accuracy and durability. Barrel is finished off with an .750" diameter F-marked Front Sight Base, PSA Classic Handguards, and an A2 flash hider.

Similar complete upper from Aero Precision (part APAR505611) - Buy now

Optional M16A4 Accessories 

Builders can always change the M16A4 configurations if the military standard issue look isn't what you're going for.

There are plenty of accessories you can check out, and here are some recommended AR15 parts

Complete Rifles

FN M16 Military Collector Edition

fn15 military collector edition

The FN M16 military collector edition rifle is by far the most up to date M16A4 civilians can purchase. It's the most modern version of the M16A4 featuring exact parts (minus FULL AUTO feature) the US military M16A4 including the UID sticker, backup sight, vertical grip and the Knights Armament handguard.

For AR builders that want the most accurate Mil-Spec M16 rifle, the FN15 is the best option next to Colt R0945.