The first time you start an AR-15 build kit, it can be quite intimidating, and going the 80% lower route can make the build just a bit more complicated. However, by the time you’re done you’ll be wondering why you were intimidated in the first place. Before you start building, or even buying parts for your rifle, you have got to decide which route to take. Meaning what kind of rifle do you want to build?
AR-15 Build Kit Buyer's Guide
A Mil Spec Build:
The Milspec standard is a classic AR-15 build kit route. It’s simplistic, easy-to-build and very effective. It is typically one of the most affordable ways one can begin for an AR-15 build, but does not slack in quality or effectiveness. Milspec simply means the parts of the rifle meet or exceed the military specifications. Milspec builds can be done in a variety of ways but the core concept is usually simplicity. Our Milspec kits specifically offer you one of the lightest options available for an AR-15 build. The point of a Mil Spec build is function over form.
A Premium Build:
A Premium build is focused more on the user’s individual preferences. As premium implies the price is just a bit higher. A premium AR-15 build kit uses the latest and greatest in AR innovations and the user has a higher level of customization options. Weight with a premium build varies per user and you can go incredibly light, or disregard weight completely and go accessory crazy. Premium AR builds will involve higher-end parts, and form and function walk hand-in-hand.
Where Do I Start with Furniture (Accessories)?:
Milspec - With a Milspec carbine and its build kit, you expect a functional piece of gear that works, and works very well. The furniture is often quite standard. A two-piece polymer forend gives you a thin and comfortable grip that is completely and totally functional. It does lack the ability to mount accessories, but it’s also the lightest option out there.
When we talk stocks, there are two ways to go with the Milspec option. The first is the old-school fixed A2 style found on M16-style rifles. It’s nice, but a fixed stock isn’t exactly versatile. The other standard is the M4 carbine collapsing stock. This simple stock is robust, lightweight, and currently serves with all branches of the United States Military. It’s simple, but it works, and best of all it's included in a few of our AR-15 build kits.
Premium Furniture - With a premium kit the sky's the limit. When it comes down to choosing furniture you have a nice selection of options available to you. The two most famous and most modular options are Keymod and M-Lok. Both systems have taken the place of heavy, uncomfortable quad rails for mounting accessories. Keymod and M-Lok both use the same idea with slightly different methods of doing so. Instead of rails covering the entire rail you can mount accessories directly to the rail system, or install small sections of picatinny rails to attach accessories.
M-Lok is more selective of who can build accessories and rails for their handguards, and have a cheaper initial investment. Keymod costs a bit more out the door, but the rail sections and accessories are more varied and often cheaper. M-Lok has been proven to be slightly stronger in retention, and has been adopted by numerous military forces around the world.
Stock options are another broad category for customization. Stocks range from the standard M4 variant we discussed above, all the way to Magpul stocks that can cost over a hundred dollars. When you are building your rifle and outfitting it with a stock, you should take a hard look at what the rifle’s purpose is. A traditional carbine, the ones that can be built from our complete rifle kits, include the Magpul MOE collapsing stock. The MOE stock is well made, easy to use, and utterly dependable.
What Kind of Bolt Carrier Group (BCG)?:
The difference between a Milspec bolt carrier group and something a bit more premium is minor. In general, a Milspec full-auto bolt carrier group is the best option for both Milspec and Premium rifles. I’m trying to be perfectly honest with you. There are bolt carrier groups that are chrome coated, or nickel boron.
Stainless steel is a good option to consider if you want to grab every ounce of accuracy out of a rifle. They are not considered Milspec though. A stainless steel barrel is not chrome lined so there could be corrosion issues if the bore is not cleaned regularly. They will also become ‘shot out’ sooner, but that still requires a massive amount of shooting. The advantages are less of a need for lubrication. However, the need is quite small and most shooters will never run their rifles to the point of noticing a difference. One other benefit of chrome or nickel boron BCGs is how much easier it is to clean. Simply wipe it down and you’re done. The biggest difference between a Milspec bolt carrier group and a premium model is the price, a premium is basically double the price of a Milspec BCG.
The Bolt carriers included in our kits are chrome lined and built to military specifications. These BCGs are high pressure tested beyond what the BCG will ever face inside a standard AR-15.
AR-15 Barrel Options:
The barrel you select for your rifle is an important consideration, both on the inside and outside. Barrels generally come in two varieties, stainless steel and chrome moly blend.
Milspec barrels are made from chrome-moly and are chrome lined. These barrels will last longer in terms of durability and rounds that can be fired. These barrels are also chrome lined and will resist corrosion. They are also easier to clean. The downsides come from the fact chrome-moly barrels are not as accurate over longer ranges.
Barrel twist is another consideration you must make. Barrel twist affects the gun’s ability to stabilize a projectile. The heavier the projectile the faster twist rate you need to stabilize it. AR barrel twists typically range from 1:7 to 1:12, and some outliers exist. 1:7 is the Milspec rate of twist and works best with bullet weights ranging from 62-to-80-grain. It’s one of the more versatile options.
If you plan to shoot the lighter 55-grain projectiles you should consider a 1:9 twist. If you go really light with shooting 40-grain round you are going to need a more specialized 1:12 inch twist barrel. 1:7 is probably the most common for a reason and stabilizes the cheap and abundant 62-grain projectiles. Although a 1:8 barrel can stabilize both 62-grain and 55-grain projectiles and both of these weights are typically the cheaper rounds.
Lower Parts Kit (LPK):
Your lower parts kit is the goods and “do-dads” that attach on and in the lower receiver that makes it function. A basic Milspec AR-15 lower parts kit is simple, easy to install, and works well. There’s nothing special about one and they can be described as effective and average.
There are premium kits by companies like Magpul that produce some extremely well made LPKs. The Magpul kit for example is nickel coated for extra corrosion resistance. This nickel coating makes the parts ‘slicker’ and give the trigger a more even and predictable break.
The Thread that Ties it All Together:
The AR-15 lower receiver is the thread that ties an entire kit together. Lower receivers come in a variety of different flavors. They can look slick and different with a billet 80% lower. Or they can be strong and proven like a forged 80% lower receiver. A forged receiver is considered Milspec and is the overall strongest option, specifically one made from 7075-T6 aluminum. An 80% lower allows you to take your build a step further as well. Having to finish the receiver yourself will truly make the rifle yours.
Using an 80% lower also allows your entire kit to be shipped directly to your home. You don’t have to go through the additional cost and wait of an FFL.
Piece at a Time or Complete Kit?:
The piece at a time method does allow you to custom tune every single part of your AR 15. If you have a particular design in your head, with very particular pieces this may be the route for you. Here you can be as picky as possible to design and build your rifle build. The downside is the price here will be higher and you have to ensure the parts are all compatible with each other. For example, you’ll have to mix an appropriate length gas system with an appropriate weight buffer.
Purchasing a complete AR-15 Build Kit is a much simpler and affordable process. You may not get the exact stock or pistol grip you want, but there are tons of different rifle kits available to choose from. Some are based on Milspec builds and others on more modern premium guns. You’ll save significant money this way, and you’ll get everything delivered at the same time. Another benefit to an 80% receiver, every single part of the rifle comes to your front door. No FFL means no FFL fees, or arbitrary waiting period.
Building an AR-15 can be a rewarding experience and you have the ability to get the exact rifle you want. It’s often more affordable than buying a traditional rifle. You can always buy a ‘sporter’ rifle quite cheaply, but when comparing mil spec and up it's always cheaper to build. Lastly it’s just fun to build a rifle. You are buying both a rifle, and the joy of building it.