AR-15: Considerations For Your Build


The below article is designed to be used as a reference guide only. It does not account for all situations and choices you have in your AR build. Links have been included in the article pointing to product pages on the Shield Group Site.

The AR-15 is widely regarded as (arguably) “America’s rifle” and, while you can buy any number of factory fresh variants, building your own tailor-made black rifle is enjoyable and well within your capabilities– and you can get what you really want.

Designed in the late 1950s by a team of firearm engineers, namely among them Eugene Stoner, at ArmaLite, then a Fairchild subsidiary. The AR-15 design was acquired by Colt and pressed into military service in order to replace the M14. At the same time, a semi auto version hit the market as a new modern sporting rifle. Since then, millions have been sold in the United States from every major rifle manufacture turning out several variants. While these options are waiting for you at, building your own is certainly possible, and can be a much more satisfying experience.

In assembling your own AR-15, you are in control of assembly, fitting, and testing. This allows the end user of determining where the money is spent.

There’s a lot to consider when building an AR-15 rifle. Mostly because there are so many different options and purposes to which you can customize.

Receivers: When you begin selecting rifle components and choosing the manufacturers, you want to start by finding a good upper and lower receiver set This is important for fit and function. Some of the Mil-Spec receivers will have enough variance to cause a poor fit. Often times the result is loose or binding components. So if possible, try to find a quality matched set from a US manufacturer, or at least make certain your upper and lower receiver will work without any of the afore mentioned problems.

When deciding on forged or billet, you may hear that forged is considered slightly stronger. Both will survive years of use without any discernible difference. So a more important consideration should be the attributes you want the receivers to have. Do you want the forward assist? An ambi-bolt release? A flared trigger guard, or an ambi-mag release built into the lower?

Lower Receiver:

The actual firearm, (serialized) and the heart of the AR-15 platform is the lower receiver. The preferred method is buying a stripped lower devoid of parts from your local gun shop — and using an FFL to arrange the transfer after a background check.

Upper Receiver:

Like your lower, you can choose any number of complete upper receiver assemblies ranging from surplus military M16A1 uppers with lots of use, to excellent new examples from Spikes Tactical, all the way to custom match grade top halves from companies such as Primary Weapons Systems or Wilson Combat that come with all sorts of goodies such as fluted barrels and full-length keymod rails. Gemtech even makes an integrated upper with a 10.1-inch barrel with a suppressor tube pinned and welded onto the end to make it 16.1-inches overall and thus a “one-stamp” NFA device.

Not regulated by the ATF so long as they are NFA-compliant, the market in uppers is very flush and competitive. Then comes the choice between

piston and direct gas impingement. While Eugene Stoner’s original AR platforms were always gas impingement, it should be noted that some of the world most reliable combat rifles, including the legendary AK 47, and M14 are gas piston-driven.

Perhaps one of the most important parts to determine performance on your AR is the barrel.


When choosing your barrel, there are basically a couple of choices with variations in the steel and hardening process. You will probably be deciding on the low alloy steel including 4140, 4150, or 4150-cmv, and chrome lined variants of each. You might choose the stainless steel barrel of 410, 416, or 416R variation. We’ll describe the characteristics of these later. The barrel forging will commonly consist of press forging which will produce a more uniform steel density barrel, and hammer forging that can create a more dense steel, but frequently with an uneven consistency throughout the barrel. Manufacturers will produce quality precision barrels from each of these methods.

With regard to rifling, the cut rifling method is typically a more expensive process used by most premier barrel makers and can lead to better precision rifling, but not always, as this method is more difficult and will produce variations that cause a lower grade for the barrel after inspection. Button rifling is an easier and cheaper process, and can still produce good shooters. The bottom line tells us that quality machining, precision honing, and rifling processes are key to a barrels accuracy. Most of the time you get the accuracy you pay for. this in not always true, because of quality control. That’s why we sometimes get a pricey poor shooter, or an inexpensive great shooting barrel.

You have control over and get what you want from the barrel. These include attributes for accuracy, weight, reliability and longevity. For example, the best precision qualities of forging, cut rifling, stainless steel, and heavy barrel profiles may give you the best accuracy, but of course, It will be heavier. Especially with a longer barrel. This may lead you to decide on fluting as a lighter option. A good chrome lined barrel may be preferably lighter, and less expensive, but they are often less accurate at longer distances due to uneven flow characteristics of chrome. This process sometimes results in a less stabilized bullet in flight. The chrome barrels will clean easier, often last longer, and still perform well, especially at the shorter distances. So this may be an option for you. Again, this goes back to what you want from your rifle.

Consider your barrel length. Do you want a shorter, lighter barrel to maneuver over longer distances? Through steep, rough terrain and brush? Or do you want a longer barrel to help increase accuracy and velocity? For example opting for a 20” barrel can give you 250 fps velocity over a 16” barrel depending on your ammunition. But then again, do you want the extra weight and length to wield around for each small increase in velocity or accuracy? A 14.5” to 22” barrel will result in a dramatic difference in weight and length, as well as possibly 450 fps in velocity and potential for better accuracy.

More barrel considerations include the twist rates, rifling, and chambering. Typically a medium twist rate around 1:8 or 1:9 is a good choice when you plan to shoot a variety of different bullet weights. By splitting the 1:7 to 1:11 recommended twist rates for the 55 to 80 grain bullets, you are averaging the optimum rate for bullet stabilization.

5r rifling (5 lands-grooves-right twist) is most common, but 4r and 6r have been used in variants with good results. 3P (Polygonal) is also an option with a couple of manufacturers. But, before saying one is best over the other, the fact is, they’re all capable of SUB MOA performance when quality machining and rifling is performed. The most common chambering options include the 5.56, the .223 and .223 Wylde.

In building your own upper, you want to make sure that you have an armorers barrel wrench, torque wrench, vice or receiver clamp and come correct with your specs for when you install the barrel, barrel nut, and gas tube. If you have never done this, you may want to consult a gunsmith or, at a minimum, do your own research.

Then comes the hand guards,or rails where you can choose rails and accessories mounts. Sights and optics are out there in a myriad of flavors. As you can see, the modularity of the AR design is it’s selling point.

Finally, you need to decide which bolt carrier group you want to go with. There are Carpenter No. 158 bolts (which are your basic Mil-spec), 9310 steel bolts (which are of a stronger steel than Mil-spec) and 8620 steel. The groups come in both semi- and full-auto profiles, both of which are legal to own, with the full-auto having a heavier bolt that generally is preferred. Chrome lining, especially on the gas keys, is a good thing. Make sure your choice in BCG is shot peened, high pressure tested and mag particle inspected.

To keep your gun running, especially while away from home in the field or range, an onboard maintenance multitool is a good investment, such as the Avid AVGTMAX Gun Tool No matter what you chose, in the end, you hold all the cards to get exactly what you want.

Lower Parts Kit: (LPK)

To your finished lower you will add a lower parts kit which generally contains a hammer spring and pin; a disconnector and spring; bolt catch, spring, plunger and roll pin; selector, detent and spring; takedown detents, pins and springs; pivot pin; buffer retainer and spring; magazine catch, button and spring and trigger guard assembly.

These parts kits can be bought complete through Shield Group Applied Military Technologies at You want to make sure you get parts that are at least Mil-spec. Also, should you be left-handed or want to be able to access your surface controls with either hand, here is where you would elect to install an ambi mag release.

The military’s technical manual (9-1005-319-23&P) which is approximately 300 pages long, is a good reference when it comes to proper assembly and disassembly. As it is a tech manual, it reads like 1980’s home Hi-Fi setup instructions, but the military spent millions developing it after generations of real-world field use, so it’s probably worth your time to read it.

The Fire Control Group that consists of your trigger components is often included in your LPK but you can choose to use a drop-in match style trigger such as those made by Timney, CMC, and others. This is perhaps the best investment you can make in the lower build as your basic Mil-spec trigger can be harsh with a grainy break, which does nothing for accuracy.

Then comes your pistol grip, which is often included in the LPK.


Which will include your buffer tube, buffer, spring, castle nut, and end plate. It’s during this process that you would install an ambi sling adapter to further customize your build.

Bolt carrier group:

When you consider your BCG you will decide on an auto/ M16 style, or semi-auto group. Many prefer the slightly heavier M16 bolt carrier to slow down the action a little, which can create more reliable cycling. This actually all depends on the barrel length, gas porting, buffer weight, and spring. It’s all a concerted effort affecting the action, and you can balance out either type of bolt carrier group for the best reliable cycling. Once again depending on the components you select, neither is best, they just have different attributes you can consider. Most of your emphasis should be placed on the quality of manufacture. The bolt should be Mil Spec, 9310 steel or carpenter 158 and MPI tested. It should have quality machining and be properly fitted, shot peened, and heat treated by a US manufacturer. Some offer a limited lifetime warranty against defects. The carrier should be 8620 steel construction with a quality coating. Nickel boron, chrome, or quality nitride treatments are a benefit to lubricity and cleaning.

Muzzle Device:

Muzzle brakes mean a great deal to the competition shooters who want every edge in obtaining speed of target acquisition. If you are concerned more with muzzle flash you may want a flash hider, or birdcage device. Also many hybrid variants will do a little of both. For example If you set up a rifle for distance with a bipod, and you’re shooting prone, some muzzle devices will cause a blast of dirt and dust preventing a speedy follow up shot.

In that case you may want to consider a muzzle brake with the most top porting to maximize downward vented muzzle blast.

Charging handle:

Don’t ignore your charging handle. It’s often difficult to grasp the handle at certain positions, or when using some mounted optics. An ambi-charging handle, lower profile handle, or side charger can offer a definite advantage in these situations.

Hand guard: You can be very creative when deciding on your hand guard or keep it simple. This is where you can really dress it up and customize it any way you want. There’s an infinite selection of designs or custom creations that are available to you. Just make sure you have the length you want for your mounted components like grip, Picatinny rail, light, front post, and bipod.

Assembly: Finally It’s important to give attention to detail when you are ready to begin the rifle assembly. Here are a few tips to remember prior to the actual build. It is best to pre-fit all components, receivers, controls, and detents to guarantee easy assembly at every step of the process. Checking headspace and any fine fit adjustments and reaming should be done at this time.

The barrel extension can be trued to the upper receiver using a receiver lapping tool. A small amount of quality anti-seizing agent and non permanent thread locker can be applied to the upper receiver threads, barrel extension, and barrel nut threads prior to fitting. That way you can disassemble it in the future without direct high heat and a five foot long cheater bar. Don’t worry; If it’s been torqued to specs, it won’t loosen on it is own.

With a new upper receiver, it’s a good practice to pre stretch the threads by torquing the barrel nut several times to ensure an accurate torque reading. Each manufacturer has a recommended minimum and maximum, usually between 40 and 80 Lbs.

No specialized tools are needed for the lower assembly, but AR specific gunsmith tools will make it easier. The upper and barrel assembly should be installed while on a reaction rod or vice block, as some of the installation steps like torquing the barrel nut can be extremely difficult or impossible without it.