A complete, assembled upper should come with everything you need to mate with a lower (in conjunction with an AR 15 lower parts kit) to create a fully functioning rifle. With that said, this short post will take a look at some of the most important AR15 upper parts and how you might want to customize while you’re working on the build.
The AR15 Barrel
First, we’ll start with the AR15 barrel, which is one of the most important parts of an AR15 upper build kit. One of the most important aspects of the AR15 barrel is its length, as this more than any other feature will impact performance. All else being equal, a longer barrel will be heavier and more stable. It will add FPS to the shot and shoot flatter, and it will offer a longer sight radius, which can improve accuracy.
The shorter the barrel, the lighter the rifle will be and the easier it will be to handle, especially in tight spaces. The other thing to consider here is that a shorter barrel, though it won’t produce the same muzzle velocities (holding all else equal) may exhibit more consistent harmonics, which can reduce barrel whip. Other things you might want to look for in an AR15 barrel is whether or not it’s threaded, as it is easier to add muzzle devices to a threaded barrel, as well as fluting, which lowers weight and aids in the barrel’s heat dissipation abilities.
AR15 Handguards
The AR15 handguard, which surrounds the barrel and shields the user’s hands from the hot AR15 barrel and gas system, is another critical component, because the handguard serves as the main mounting interface for shooting accessories. There are three main types of AR15 handguards, each of which offers unique benefits and drawbacks. Arguably the most common (and one of the oldest) is a Picatinny rail handguard. The Picatinny rail is one of the heaviest, but it also offers the widest compatibility with shooting accessories.
Then there are KeyMod and M-LOK rail systems and AR15 handguards, both of which are lighter and more comfortable in the hand than Picatinny rails. They offer a good range of compatibility with shooting accessories, but the tradeoff is that there are not as many accessories made for them as there are for Pic rails.
AR15 Muzzle Brakes
AR15 muzzle brakes are a class of muzzle device that also offer a lot of value with an AR15 upper build kit. The thing is that most build kits don’t come with them; they come with a different type of muzzle device known as a flash hider. There is a world of difference between AR15 muzzle brakes and flash hiders. The primary purpose of a flash hider is to obstruct the muzzle flash, which prevents blinding the operator, thereby preserving the sight picture.
That is not the purpose of an AR15 muzzle brake. A muzzle brake is designed to change how the gasses are ported at the muzzle, which can considerably counteract the forces of felt recoil. In some cases, a muzzle brake can cut felt recoil by as much as 50% without adversely affecting shot power, which makes this a valuable swap to make while you’re customizing a rifle build.
The AR15 BCG
Let’s also talk about the AR15 BCG, or bolt carrier group, which in many ways is the “heart” of the rifle. The bolt carrier group carries the bolt (hence the name) which in turn houses the firing pin and extractor, as well as the gas key which siphons off gas from the gas system, enabling autoloading operation. The main thing to consider with an AR15 BCG is the coating. Most AR15 upper build kits that come with a bolt carrier group (not all do) come with a mil-spec BCG, which means it will be phosphate coated.
A phosphate-coated mil-spec AR15 BCG has some selling points. For one, it is an affordable option, and it also has a non-reflective surface which is good for purposes of concealment. Beyond that, it has a bit of tooth which means it will require more liquid lubricant. There are advanced AR15 BCG coatings, such as black nitride, titanium nitride, diamond-like carbon (DLC), nickel boron, and a few others that, while much more expensive, exhibit superior permanent dry lubricity, which means that they require less liquid lubrication.
AR 15 Lower Parts Kits
It should also be noted that most AR build kits do not come with a lower receiver, as that is the part that is serialized and considered a “gun” by the ATF. That is one part you will need to buy separately, and it will require an FFL transfer. If you buy an AR15 upper build kit and a separate, stripped lower, you will also need an AR 15 lower parts kit to complete the build. Generally speaking, AR 15 lower parts kits contain all the parts and hardware, including pins and fasteners, needed to complete assembly of a lower receiver before mating it to an assembled upper.
Your Next AR15 Upper Build Kit Is Here
Hopefully you found this short guide helpful. If you’re looking for AR15 upper build kits or parts, check out our full catalog via the links in this article, and if you have any questions about part specifications, features, or compatibility, get in touch with us at Sales@MCSGearup.com.