HK416 Clone Build: Brownells BRN-4 Upper and STS416 A1 Lower

The HK416 is one of those iconic AR-15s that has become legendary due to its use by Tier 1 groups across the globe. Ask Delta Force about the HK416, a Navy SEAL, or Osama bin Laden. Oh, wait. You can’t. They will tell you the HK416 rifle is built like a tank. Owning a real, bona fide HK416 is expensive. Building a clone is a route you can take, but be forewarned, building an HK416 clone is easy; deciding what HK416 variant you want and how close you want it to an original can send you down a rabbit hole. I made it easy and opted for a Brownells complete upper and an STS lower to build an HK416 that performs and looks like an original.

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The basic difference between an M4 and an HK416 is the operating system they use. The M4 uses the standard gas impingement system that’s equipped on AR-15s and M16s since the 1950s. The HK416 uses a short-stroke piston-driven system. There are other differences, but that’s the main one. In the 1990s, the Army’s Delta Force worked with Heckler & Koch to develop a new carbine for door kickers to use in a close-quarters environment. Delta Force wanted a compact AR platform that could handle longer strings of full auto fire, and they wanted it to run cleaner so there would be fewer malfunctions. It also needed to be more suppressor-friendly, and it shouldn’t be any heavier than a standard direct impingement AR.

H&K took the gas piston route in the HK416 design because decreasing the barrel length on a piston AR does not pose the reliability and performance issues as it can when the barrel is shortened on a direct impingement gas system gun. Piston guns also run cleaner than a direct gas gun, so there is less fouling and less time is needed to clean the gun.

The Brownells BRN-4 is built by Faxon for Brownells and features a 5.56x45mm NATO chamber and a bore with a 1:7-inch twist rate. The muzzle is threaded 1/2-28. You can get the BRN-4 in 16, 14.5, and 10.4-inch lengths. I opted for a 14.5-inch, and yes, I needed an SBR tax stamp. The barrel contour is heavy or medium. The gas block is specific to the barrel length and designed to vent gases forward.

The upper receiver is made from a billet and machined to look like a forged receiver. It includes a BCG, a mil-spec charging handle, and a Magpul ejection port cover. This upper replicates the HK416 upper and is a fraction of the cost of a real one. Original HK416s used an A2-style birdcage flash hider, but I wanted to give my HK416 clone my own twist, so I used a Strike Industries Cloak flash hider, which features four tapered prongs. It’s lightweight and compact.

STS (Specialized Tactical Systems) manufactures variants of HK416 billet lowers that are dead ringers for HK416 A1, A3, A5, and 416C variants. The A1 is the original and doesn’t accept all mags because of the 416 magwell profile. The A5s introduced ambi controls as well as a typical AR magazine profile, so it will accept all magazines, including PMags. The 416C lower is modeled specifically after the ultra-compact HK 416C, Heckler & Koch’s prototype Personal Defense Weapon (PDW).

The A3 lower features the classic HK416 A1 design with A5-style ambidextrous controls. Rob at STS really took the time and effort, and used input from users on the HKpro.com forum in developing the lower to get the lower dimensionally and aesthetically matched to the original HK standards. Even the font on the serial numbers mimics the HK. Actual HK logo markings are not included for legal compliance, but if you must have the HK logo, BlackOps Defense will engrave the STS lower so that even the guys and gals in Oberndorf am Neckar in Germany will not know the difference.

STS rolls mark the required markings on the inside of the trigger guard. You have to look to find it. With all the different variants, it really depends on what era you want your clone to be built for. This is the start of the rabbit hole experience. I did my research and went old-school with an A1 variant since the Brownells upper doesn’t have the ridge on the left side of the upper for the ambidextrous bolt release that was incorporated into the A5 variant.

I wanted my HK416 built to look a little retro and close to an HK416 A1, so I sourced an E1-style buttstock with the convex butt pad, a 9-inch quad rail, and the classic HK battle grip. I found all these parts on the H&K USA webstore, but parts can be sourced elsewhere. Depending on how deep you go down the rabbit hole, the STS will accept any mil-spec AR-15 lower parts.

Some features on the HK416 are HK-specific, such as the buffer tube assembly. The HK tube is military spec. It has drain holes built into the end and the bottom edge. It also has bearings along the bottom to reduce buttstock rattle. The buffer retainer is also pinned in place, unlike a standard AR.

I wanted to make use of most of the HK416 features, and since the STS lower is as close to an HK lower as you get. I bought a used HK416 lower parts kit from Blue Mountain Supply. The kit includes a trigger assembly, bolt catch assembly, selector switch, and all the springs and detent pins you need to finish the lower build. You can find used HK416 lower parts kits online.

You could easily attach the Brownells BRN-4 to nearly any AR-15 lower receiver and be good to go, but it would only be a fraction of the HK416 experience. In my opinion, if you are going through the build, spend some extra Benjamins to get real HK parts. 

If you have built an AR-15, then building an HK416 clone is very similar. You will need a hammer, roll punches, a castle wrench, and a few other tools. It took me a few hours to assemble the stripped lower, and that was with a break with a nice Maduro with a Connecticut wrapper.

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I’ll probably go with an EOtech holographic sight, but I had on hand a Burris FastFire E red dot. This is an enclosed emitter-style sight design for handguns and is just as handy on an AR-15 style rifle. The Fastfire E has the same footprint as an Aimpoint ACRO, and it is equipped with a 3.5 MOA dot. There are red and green dot reticle versions. I have the red dot.

The feature I like about the FastFire is that it is always on and ready for action, running on a CR2032 battery with about 60,000 hours of battery life. I’ve also come to prefer closed emitter dot sights since dust and debris can’t interfere with the optics’ performance. It also automatically adjusts to light conditions, plus there are eight brightness settings. These are two other features I’ve come to expect on a red dot. The viewing window is large and allows for two-eye aiming.

So, how does the HK416 clone run? Is it a fraction of the cost with a fraction of the performance? No, not with my first impression. What you notice right away with a piston system AR is that it’s heavier, and the balance of the rifle is more toward the muzzle. The rifle cycled smoothly; it ejected at the 3 o’clock position. I dumped a few hundred rounds through it using steel and aluminum magazines, and I had no issues. Running drills with reloads, the HK416 clone ran well. Recoil is different than a mid-length gas gun since you can feel the piston doing its thing. I’m going to continue running the Brownells BRN-4 and STS lower clone build. My initial impression is that this may be a clone, but it sure doesn’t act like it.

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