AR15 Parts - What To Consider Before You Buy

AR15 Parts – What To Consider Before You Buy

E2 | Quality AR-15 Parts

It’s been a whirlwind for the firearms industry over the past few years, and 2022 is continuing the trend. Those who already own an AR may be considering upgrades, or taking the leap and building their own AR15.

A simple Google (or Brave if you’re feeling the freedom!) search for AR15 parts will generate many results. From parts treated with titanium nitride to items that are phosphate-coated, there are options for the motivated patriot.

But, like with most things in life, there are quite a few factors at play.

So, with regards to AR15 parts, what to consider before you buy?


A modern defensive rifle like an AR15 is the culmination of decades of research and refinement. Eugene Stoner’s direct-impingement system has stood the test of time with these advances.

An AR15 rifle has a simple task, but the devil is in the details. The idea is to contain an explosive force, and propel a 5.56mm or .223 projectile downrange in the desired direction. The term “explosive force” is where the science comes in. Every AR15 part is subject either to the direct pressures of that explosive force, or the transmitted recoil. AR15 parts have a lot of work to do, repeatedly and rapidly.

Before purchasing your AR15 bolt carrier group, barrel or receiver, one must first look at the composition of the part. While there is a variety of materials out there, some benchmarks can be utilized to assist in the purchasing process.

The most durable and strongest materials should be present in the critical working components of your AR15. Parts such as the bolt carrier group, the barrel, the lower receiver, and the upper receiver take the brunt of the force. Visualizing the explosive force can help one think about the pressure being delivered while the AR15 is in operation.

A quality BCG will have the carrier machined from 8620 steel, with the bolt proper machined from 9310 steel. This should be considered the bare minimum for a reliable BCG. As a finishing touch, a quality bolt carrier group such as those from E2 Armory will sport a parkerizing or nitride finish for wear resistance.

AR15 parts need to be reliable.

Another critical AR15 part, of course, is the barrel. This essentially contains the explosive force of the detonating cartridge and directs the projectile downrange. A 5.56x45mm projectile subjects the chamber of the barrel to a pressure spike of around 55,000 pounds per square inch. Thus, an AR15 barrel needs to be made from some truly impressive materials. Barrel manufacturing is both a science and an art. But, there’s a standard one should look for when purchasing an AR15 barrel.

An AR15 barrel rated for duty use will be hammer-forged from a chrome-moly vanadium alloy, with the bore and chamber being chrome-lined for corrosion resistance. Military-spec barrels are all subject to this process and are more than suitable for citizen use. An alternative process treats the barrel steel in a nitride process, which actually imbues nitrogen into the steel. Nitride treatments are a newer process and barrels manufactured this way generally exceed military specifications for accuracy. However, chrome-lined barrels have shown to be more durable when subject to extreme abuse, i.e. sustained full-auto operation.

Though not subject to high pressures, the upper and lower receivers of an AR15 should be analyzed. AR15 upper and lower receivers should be forged from an aluminum alloy such as 7075 and tempered to a T6 rating. Those found for purchase at E2 Armory meet and exceed these specifications. Lightweight, yet durable enough to withstand everyday handling and the shock of firing. These AR15 parts have a key role in the performance of your rifle, and thus should meet this standard.

Other components such as the buffer tube and handguard will often be made from 7075 T6 as well.

When purchasing AR15 parts, ensure that the components meet the standard for metallurgical makeup.

AR15 parts can be composed of quality materials, but if the essential manufacturing processes are flawed, there will be problems.

Testing procedures

AR15 parts can be composed of quality materials, but if the essential manufacturing processes are flawed, there will be problems. Manufacturers will go to great pains to test their AR15 parts for reliability and publish those results. This is where the term “mil-spec” pops up, where military users require products to be tested according to procedure.

One thing about mil-spec is that the term means a given component meets a military specification, which may or may not fall within the acceptable performance parameters of the end-user. This is often why one will see the tagline “exceeds mil-spec” applied to certain brands of AR15 parts, such as those from E2 Armory.

Testing procedures vary based on component, but one common test is a high-pressure test, aka the HPT. The part in question is subject to pressure far greater than normal, i.e. by test-firing with a proof round. If the part shows no signs of failure or stress, it passes the test.

Following the HPT in the testing sequence is the magnetic particle inspection test. Simply put, the part in question is coated with an iron-based solution, that glows under ultraviolet light. Then the part is put into a magnetic field, and the iron solution orients itself accordingly. Since gaps of air do not support the field, the solution drips through and shows under the light, in the form of bright lines, indicating flaws.

A quality manufacturer of AR15 parts such as E2 Armory will list that their parts are HPT/MPI tested.

Mil-Spec AR-15 Uppers, AR-15 Lowers & Bolt Carrier Groups. Free Shipping Every Day

Specific Considerations For Common AR15 Parts

Beyond composition and testing, other details must be considered, which are specific to the part in question.

For example, when purchasing a bolt carrier group, the seller will denote that it is “full-auto” or something similar. This does not mean that it turns a standard semi-automatic AR15 into a fully-automatic rifle. For that to happen, several other components are needed, which fall beyond the scope of this article. When a bolt carrier group is labeled as “full auto”, it merely means that the bolt carrier group is capable of being fitted to a fully-automatic M4 or M16 rifle. The full auto BCG is slightly longer and heavier than a semi-auto BCG. The benefit to a semi-auto AR15 is that the mass of the full-auto BCG reduces felt recoil, as well as wear. Most BCGs made at this time are of the full-auto variant.

Of course, there are considerations when selecting an AR15 barrel. The biggest factors are gas system length and twist rate.

The gas system of an AR15 captures some of the gas from the firing sequence through a port in the barrel with a gas block, sends it back through a gas tube into the bolt carrier group, forcing the BCG back to cycle. Gas systems usually come in 3 configurations: carbine, mid-length, and rifle length.

Carbine length gas systems are the shortest, and since they tend to provide the AR system with the shortest dwell time, which is the delay from when the bullet passes the gas tube hole to the time the bullet exits the barrel. This system is no longer favored since it tends to run the AR harshly.


Mid-length gas systems are preferred, as they provide enough dwell time to cycle the AR15 action, and still keep the system pressure low enough to minimize excess wear.

Rifle-length gas systems usually appear in barrel lengths of 18 inches or greater, and thus one will only find them in specific setups such as designated-marksman AR15s, and retro AR15s which sport a 20-inch barrel.

Concurrently, the twist rate of the barrel must be considered. A rifle barrel has spiral grooves which impart spin into the projectile as it travels. The twist rate of an AR15 barrel, or any other firearm barrel, is denoted in inches. For example, 1:10″ means that the projectile is spun around once over a distance of 10 inches.

Spin stabilizes the projectile, ensuring more accuracy. Heavier projectiles require faster spin rates. For example, a barrel with a 1:12″ twist rate will stabilize a classic 55 grain 5.56mm M193 projectile, but will not work for the modern 77 grain Mk262 Mod 1 5.56mm round. For that heavier cartridge, a 1:7″ twist rate is required. In general, an AR15 barrel should have a 1:7″ twist rate.

Along the same lines, checking an upper receiver for M4-style feedramps should be part of the process. Extended feedramps assist in feeding the newer 5.56mm ammunition into the barrel chamber of an AR15, lessening the chance of a jam.

Brands Shouldn’t Be The Sole Consideration

There’s a lot of hype and promotion behind the big brands of AR15 parts. Second Amendment social media is awash in promotions for those marques. However, in some cases, one is merely paying for the rollmark. It’s no secret that some brands only apply the finishing touches to AR15 parts, and etch their logo on the side. Machining AR15 parts is a very exacting process, and there exists only a small number of facilities capable of producing these components.

If one is looking to shop for AR15 parts, it’s worth the time to research who the OEMs for the popular AR brands are ( is an excellent option). Industry secrecy makes tracing the supply chain difficult, but sometimes, one can score a nugget of useful data. If the source of the component is from a major OE manufacturer such as AO Precision, one can be assured of the quality of the AR15 parts. The part may not be a big Tier 1 brand and may lack the go-fast finish, but the component will perform to spec, especially under duress.

There Are Many Factors To The AR15 Parts Purchase Equation

To be fair, there’s a dizzying array of considerations to purchasing quality AR15 parts. Material composition, testing compliance, and technical specs can all be rather confusing. Once one drills down and ensures that the AR parts in consideration meet some basic industry benchmarks, the AR15 parts purchase process becomes a simple affair.

E2 Armory is a leading retailer for Ar15 parts based in Daytona Beach, Florida. Their AR15 parts are mil-spec, made in the USA and they offer free shipping. Check out the website for incredible prices every day

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