August 02, 2022
In a world of AR-15 and AR pattern rifles, what makes one stand out from the other? Is it materials, quality control or appearance? The answer is a resounding "all of the above". It takes a keen eye and a bit of research though to separate the "wheat from the chaff" so to speak. Some parts are frankly better than others, and it isn’t always the part that is more expensive or wearing the Gucci name. What I am going to share here are a few proper building techniques, tips, and tricks while building an enhanced AR-15 pattern carbine using GunNation LLC's GN15 billet small frame receiver set.
The GunNation billet 7075-T6 receiver set will serve as the foundation for my build. While GunNation LLC is relatively unknown to the AR market (as they are new, my set is serial number 11), the company’s owner, Justin Michaud, is no stranger to the firearm and AR world. A gun shop owner and NFA/Class III dealer out of Lake Stevens, Washington, Mr. Michaud has years of experience behind the pattern. Recently he set forth to add subtle design features to an AR-15 receiver set that would make for a more "user friendly" rifle. When initially contacted, I was preparing to refit a White Oak Armament (on a Pac-Nor blank) 16-inch target rifle with a new receiver set. The old forged "A3" upper receiver was just not well-suited to the barrel and LaRue MBT trigger combination. In short, it was time for an upgrade!
A quick examination of the GunNation billet receiver set was positive. While a factory-matched set, both upper and lower came individually packaged and well protected by two layers of bubble wrap. The packaging was nice, professionally done and I found the "we appreciate you" on the inside opening flap quite a nice personal touch that is sometimes forgotten. The receivers are machined from 7075-T6 billet and feature a Type III hardcoat anodized finish. They are both nicely machined and quite smooth, with minimal machining marks found on both the upper and lower.
Both the upper and lower are cut with weight savings in mind. They feature weight-reducing relief milling on both upper and lower receivers, which sets well with the modern "lightweight rifle" trend. The upper receiver lacks the auxiliary bolt closure mechanism, colloquially known as the "forward assist". I like how these receivers are machined without the forward assist, as I find this device unnecessary, it further reduces the overall weight of the rifle and provides a cleaner, sleeker look and feel. While I like the fact that GunNation removed the forward assist, I’m glad they retained the dust cover. I do find the dust cover a necessity, as it helps keep larger pieces of foreign debris out of the rifle. The only other companies I’m aware of that will offer this combination are CMT and Vltor, with their MUR-1S. I don't understand the reasoning for companies to remove both, but I like that GunNation LLC included the dust cover.
While touching on the subject of the dust cover, GunNation slightly redesigned the attachment point for the dust cover. They created a fully supported channel in which the dust cover rod is placed. The likelihood of snapping the rod off (which I have done) is eliminated, while also eliminating the need for the corresponding "C clamp" which secures it into place. I found this, while small, an upgrade to the original design and well thought out.
The upper to lower fit is nice overall and substantially tighter than that found on many Patrol rifle offerings, Colt LE6920s or FN's civilian rendition of their M4 Carbine. While not Mega Arms’ tolerances, the GN15’s tolerances are held on the higher end of the TDP (Technical Data Package). Plus, it does feature a tensioning screw to further solidify the receiver fit.
Barrel installation was completed after squaring the upper receiver. To accomplish this I used an upper receiver lapping tool from Pacific Tool and Gauge (PTG). This squares the interface between the upper receiver and barrel extension shoulder, thus creating a square, consistent and uniform mating surface between barrel and upper. Minimal squaring was required and the upper receiver was largely square from factory.
When bedding the barrel to the upper (yes, I bed the barrel) I typically use Loctite 620, which is a high heat, high viscosity, anaerobic sleeve retaining compound. This is typically the best compound to use and is a more modern take on US Army Reserve Marksmanship Program Service Rifle Team armorer Joe Carlos's Loctite bedding procedure. I will be using traditional Loctite 242 (or, my preferred Permatex variant) for this rifle, which is more of a traditional approach.
The mistake many people make is they assume the Loctite is "locking" the barrel in place and that the residual heat from firing the rifle will cause the Loctite to deteriorate and fail to function. This isn't the purpose of the Loctite. The purpose (in bedding a barrel) is to act as an anaerobic sleeve retainer, fill any voids or inconsistencies between the upper receiver and barrel extension interface. For more information on this subject, please view Joe Carlos's findings on accurizing the AR pattern rifle.
I also fit the barrel through thermal means (thermal fitting) to further enhance accuracy. This is easily achieved through use of a commercial heat gun or propane torch. I prefer the heat gun, as heat can be liberally applied and is more controlled. It also is harder to damage the finish or damage the integrity of the upper receiver. What "thermal fitting" does is it expands the structure of the aluminum, allowing the material to open a couple of thousandths of an inch. Aluminum has a lower heat tolerance than steel, thus meaning the aluminum will expand quickly, allowing the Loctite-covered barrel extension to easily slide into the upper receiver.
As the aluminum cools however, the interface between the upper receiver and the barrel extension will shrink back to its original size, closing around the barrel extension. This perfectly mates the barrel to the upper receiver, making the rifle noticeably more accurate. The need for thermal fitting is typically found in premium receivers with tight tolerances and a definite positive on the billet GN15 set.
One notable feature I like is the "3 leaf clover" pattern gas tube opening on the upper receiver, over the more traditional "4 leaf clover" approach. This makes properly centering the gas tube much easier and seems slightly more robust, as more material is placed around the tube itself. On the upper receiver, I thought the face of the upper (located below the Picatinny rail) could have been machined down a bit more. There were noticeable machining marks here (shown in the photos); while this is strictly cosmetic and would be covered up by any rail system, it is worth noting.
The barrel nut threads were smooth, consistent and showed no imperfections, metal burs or inconsistencies; making a professional barrel installation easy. The rifle build completed without a hitch and looked better than I hoped it would in both the aesthetics department and tolerance department. This is largely due in part to the solid foundation from a nice 7075 billet receiver set. I was highly impressed with the machining quality, quality control aspects, high tolerance levels and overall fit, as well as finish.
While not "perfect", as some machining marks still remained in hidden areas and I found the finish almost dry and "powdery", these things are trivial at best and I find it easily surpasses some of the "big name" receivers and offerings on the market. Overall, this build went well, was fun and I enjoyed working with the premium receivers offered by Mr. Michaud and GunNation LLC. With an MSRP of $369.00, hobbyists and builders alike should take note. For more information visit GunNation.com.
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About the Author
Michelle Hamilton has a Bachelor’s degree in Criminal Justice/Homeland Security, is a serious student of wound ballistics, military history, small arms design and manufacturing and is a competitive shooter.