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The Beginner's Guide to The AR-15: The Basics

The Beginner's Guide to The AR-15: The Basics

Posted by on May 1st 2020

We've got loads of information about building an AR-15. But if you're a first-time builder, all that info can feel overwhelming. This simple, shorter guide introduces the basics of the AR-15  and acts as a starting point for buying and building your first rifle. We'll gives you links to the more in-depth guides for each part of the AR, so you can become a master of the parts and firearm as whole while you learn.

What is The AR-15?

The AR-15 is a gas-operated semiautomatic rifle developed by weapon designer Eugene Stoner in the 1950s for the U.S military. Fielded in Vietnam as the M16A1, the rifle was continually updated and earned popularity in the civilian market over the following decades. Today, the AR-15 is the single-most popular firearm sold in the United States as of 2020. The NRA estimates that well over 8,000,000 ARs (nicknamed "black rifles") were in ownership two years ago. That number is estimated to be over 11,000,000 today. There are plenty of reasons why the AR-15 is the most popular firearm in 2020 (and why you probably want to build one).

AR-15 FAQs

The AR-15 has so much info swirling around it, it's tough to find the real answers to common questions. We tried to answer the questions you're most likely wondering about.

Is the AR-15 illegal?

No. The 1994 Assault Weapons Ban temporarily banned AR-15s, but this was allowed to expire ten years later. Congress found no significant crime data backing the ban, as firearm crime rates generally remained the same during the ban. Some states have placed restrictions on the AR-15 to make its typical semiautomatic, 30-round-magazine configuration illegal.

Can I order my AR-15 online?

For the most part, yes. The only part of the AR-15 that is considered a firearm is the stripped lower receiver. All other parts, including the upper receiver, barrel, parts kit, buttstock, gas system, and all other parts are not considered firearms. They can be purchased online and shipped to your home. Most choose to order a rifle kit or pistol kit, which can be purchased without the firearm component. Some choose to fabricate their own receiver from an 80% lower.

What is an 80% lower?

This is an unfinished stripped lower receiver for the AR-15. The 80% lower lets you complete your AR-15 by cutting and drilling the receiver yourself. Until you've taken these steps, the 80% lower is not legally considered a firearm. This is an alternative to buying a stripped lower and paying the extra fees associated with buying a firearm. This is legal to do under federal law, but some states have placed restrictions on the practice.

Read the full guide on 80% lowers here.

Is the AR-15 an "assault rifle"? 

No. An assault rifle is a select-fire, fully automatic weapon (machine gun) in service with militaries, police, and defense organizations. The AR-15 is a semiautomatic rifle. It is no different, legally or in naming, than any other semiautomatic weapon you'd buy or build.

Can the AR-15 be made fully automatic?

No. The AR-15's lower receiver is manufactured in such a way that an M16 or M4 (full-auto) parts kit cannot be installed without extensive modification. Federal law prohibits the sale of machine guns to the general public, too. You need a special firearm dealer license to possess a machine gun or machine gun parts.

What's the minimum legal barrel length?

16 inches. Any rifle with a barrel shorter than 16" is considered an SBR (short-barreled rifle), or a pistol if it does not have a buttstock.

What's the minimum overall rifle length?

Your AR-15 must measure (barrel included) at least 26" in overall length. If your rifle measures less than 26", it will be considered an SBR or pistol if no buttstock is equipped. The ATF covers barrel lengths and weapon lengths in the National Firearms Act Handbook.

What does "AR" stand for?

It does not stand for "assault rifle". It stands for "ArmaLite Rifle", named after the company who sponsored Eugene Stone, its inventor.

What are the AR-15's available calibers?

There are well  over 50 calibers now available for the AR-15 platform. The most common calibers are 5.56 NATO, .223 Remington, .308 Winchester, 9mm, .22 LR., .243 Winchester, 6.5 Creedmoor, and 300 Blackout. 

Is the AR-15 a good hunting rifle?

Yes. Many hunters have traded traditional bolt guns for AR-15s. The plethora of calibers paired with semiautomatic fire, light weight, and high accuracy make the AR-15 the perfect hunting rifle. Chambered in 5.56/.223, the AR-15 can take smaller game like coyotes, hogs, goats, and small deer. Chambered in .308, the AR can take most North American big game.

What is the AR-15's effective range?

Between 400 and 600 meters. Most experts agree that a 12" target can be reliably hit repeatedly at this distance with a 5.56 NATO or .223 Remington cartridge. AR-type rifles chambered in .308 Winchester or 6.5 Creedmoor can easily shoot at distances reaching 800 meters or greater. ARs chambered in 300 Blackout or pistol cartridges can hit targets at 100 to 300 meters.

Why Build an AR?


The standard AR-15 is most often chambered in 5.56 NATO or its commercial equivalent, .223 Remington. Both cartridges have been developed and improved for half a century through wartime, competitions, and precision marksmanship, leading to amazing ballistic performance with wide availability in parts and ammo. In its usual configuration with a 16" barrel, the AR-15's lightweight, compact, easy to aim and fire, and exhibits minimal recoil with high capacity.


Because the AR is so popular, manufacturers and parts makers cater to the market more than any other firearm model. Endlessly available barrels, receivers, handguards, trigger kits, and accessories mean you can build an accurate, reliable, "military-spec" AR-15 for under $500. And all that ammo? With so much available, ammo can be purchased for as little as $0.23 a round. That's less than $5 for a small box of ammo.


The saturated parts market means you can configure your AR-15 in literally thousands of different ways. Innovations have brought things like folding buttstocks, custom piston systems, carbon-fiber barrels, lightweight plastic receivers, and new calibers like .308 Winchester (7.62x51 NATO), 6.5 Creedmoor and 6.8mm SPC for precision shooting, big, hulking rounds like .458 SOCOM and .50 Beowulf, even pistol cartridges like .45 ACP and 9mm. You can build a 28" bench AR-15 that'll shoot 1,000 meters, a super-compact 9mm AR pistol that measures barely 16", and everything in between without spending an arm and a leg.


With over 50 years of designing, testing, and upgrading on its books, the AR-15 is one of the most reliable firearms ever developed. Its simple and well-established design means even entry-level models are capable of firing thousands of rounds with consistent performance and few to no failures of any kind, with great accuracy. 

Building an AR-15 is easy

That's probably why you're here. Building an AR-15 requires just a few common tools, even if you assemble your rifle part by part. Let's see what you can build first.

Most Common AR-15 Configurations

Standard 16" Rifle (5.56/.223)

This is the most popular AR-15 configuration. The standard rifle setup you'll see on most kits or assembled guns includes a 16" barrel, carbine or mid-length gas system (we'll get into that later), and a typical "military-spec" parts kit. The parts kit contains the trigger, hammer, safety, and internals for the lower receiver to function. Iron sights are the norm, here. Front sights will either mount to a railed handguard, or be integrated into the gas block itself. A typical adjustable buttstock is included for shouldering the rifle.

Rifle chambered in .308 ("AR-10")

The AR-10 is technically the original AR-15 design. Eugene Stone converted the .308 rifle to fire 5.56 NATO after it was initially designed. Today, many builders or buyers refer to this rifle setup as an AR-10, though the modern .308 AR is based on a platform designed by  DPMS Panther Arms called the LR-308. It almost exactly matches the AR-10's design, but there are slight differences in how certain parts are sized and shaped. This setup is popular among precision shooters and North American hunters.

AR-15 Pistol (or SBR)

The minimum legal length of any rifle's barrel is 16". The AR-15 can be legally configured as a pistol with a barrel shorter than 16" if you don't install a buttstock. If you wish to use a buttstock, you will need to register your new AR-15 as a short-barreled rifle with the ATF. AR pistols instead come with something called a pistol brace. You can  learn about the legality of shouldering a pistol brace here. AR pistols can be chambered in 5.56/.223, though 300 Blackout and 9mm are popular with this configuration.

Building an AR-15: What's Needed?

If you want to build an AR-15, you may not even need tools. Most AR parts come pre-assembled, requiring you to simply connect them together before you hit the shooting range. These are the two main parts you can purchase that require no tools for assembly:

Upper Receiver Assembly

The  upper receiver assembly includes: 

  • Stripped upper receiver
  • Barrel and chamber
  • Bolt carrier group
  • Charging handle
  • Front sight post
  • Gas system
  • Handguard

This assembly attaches to the lower receiver assembly via two large pins. 

Lower Receiver Assembly

The  lower receiver assembly consists of the: 

  • Stripped lower receiver
  • Buttstock or brace (if pistol)
  • Trigger, hammer, and safety
  • Pistol grip
  • Buffer tube
  • Recoil spring 
  • Buffer

You can purchase these two halves and configure a custom rifle in about one to two hours. Most builders purchase a full upper assembly, and install the lower parts kit (hammer, trigger, safety, pistol grip, and buffer tube) onto the lower receiver. We've got guides below to help you with those steps!

Here's your first big, technical guide: The Builder's Master Guide to AR-15 Parts

This master guide breaks down every single part you need to build an AR-15 from scratch. It also details the function of each part. We've also got information to cover each of those major components in greater detail. You can use each resource below to learn, in detail, what configuration is best for your new AR-15. We'll cover a "short n' sweet" version of the typical gold standard setup below, too.

Optimal AR-15 Setups

Three parts on your AR-15 will determine performance and reliability: Barrel length, barrel twist rate, and gas system length. These are the optimal setups for each common caliber:

5.56 NATO, .223 Remington

Twist Rate: 1:7 to 1:9. The 1:7 twist rate is the most universal for virtually all 5.56 NATO and .223 Remington loads. It handles heavier bullets (77-grain) for hunting and precision shooting, but it stabilizes the most common 55-grain and 62-grain bullets just as well. If you're sticking to shooting only those lighter bullets, a 1:8 twist or 1:9 twist is optimal. 

Gas System: Carbine or Mid-Length. The carbine gas system is the most common type of system found on most 5.56/.223 ARs. It's the most reliable, providing guaranteed cycling of the bolt carrier group even when the rifle is dirty or filled with dust and mud. Carbine gas systems are technically "over-gassed", so the recoil they produce will be more noticeable than a mid-length gas system. The mid-length gas system is incredibly reliable, too, but slightly reduces felt recoil. 

Barrel Length: A 16" barrel provides optimal velocity for both 5.56 and .223 cartridges for AR-15 rifles. Longer barrels will provide negligible and unnecessary increases in velocity. AR-15 pistols can have barrels as short at 7.5" while providing favorable accuracy at 100 meters or more. When building an AR pistol, simple logic says the longer the barrel, the more accurate your pistol will be at greater distances.

.308 Winchester

Twist Rate: 1:10 to 1:11. The 1:10 twist rate is the most popular for .308 ARs because it handles the widest variety of ammo (147-grain to 180-grain) with the most accuracy. Virtually all factory match-grade .308 ammo is 168-grain, and 1:10 does an excellent job of providing high stability for this round without sacrificing performance of lighter or heavier bullets. If you'll be sticking with heavier bullets most often (180-grain or higher), the 1:11 is a better choice.

Gas System: The extra powder and energy produced by the .308 cartridge requires a longer rifle-length gas system. Short gas systems (like mid-length) will be too over-gassed and could result in a critical failure of the rifle. 

Barrel Length: The .308 cartridge requires a longer barrel than 5.56/.223 to achieve optimal velocity, but not by much. Most ARs chambered in .308 use a 20" to 24" barrel. A 24" barrel only adds, on average, 80 extra feet per second of velocity compared to a 20" barrel. At 20", enough velocity is achieved to provide optimal performance.

9mm Parabellum

Twist Rate: 1:10. This is the single most effective twist rate for 9mm cartridges. It'll reliably stabilize and provide accuracy for bullets weighing anywhere from 90 grains to 150 grains. 

Gas System: None! The 9mm cartridge uses blow-back energy to cycle the bolt. No gas system is required on an AR chambered in 9mm.

Barrel Length: A 12" barrel provides the highest velocity with the shortest possible barrel length for 9mm. Anything longer provides negligible increases in velocity. Since 9mm was designed to burn its powder quickly and achieve velocity in shorter handgun barrels, one can go as short as 8.5" and still enjoy high accuracy at 100 meters. 

We wrote an entire guide on the optimal AR-9 configuration.

300 Blackout

Twist Rate: 1:7 or 1:8. The 300 Blackout cartridge is designed to fire as a lightweight supersonic and heavy subsonic round using a single configuration. To do this, a fast twist rate like 1:7 or 1:8 is required. These rates will stabilize the heavier sub loads without over-stabilizing supersonic loads. 

Gas System: Pistol-length. This is the only reliable gas system for 300 Blackout. These heavy rounds use small cartridges and much less powder compared to other .30-caliber rounds, so the shortest possible gas system is required to cycle the bolt with both loads.

Barrel Length: Because 300 Blackout cartridges burn their powder quickly like a handgun cartridge, a short barrel is sufficient. Ballistic data says a 9" barrel is optimal, but shorter 7.5" or 8" barrels will suffer only negligible losses in velocity and accuracy. 

Here's an in-depth guide on building the optimal 300 Blackout AR.

Federal vs. State Laws And Building an AR

Some states have banned AR-15 kits, certain AR-15 parts, 80% lowers, and certain other firearm parts, or have otherwise restricted the sale and ownership of products we sell. So, be sure to check your local and state laws. We can’t ship our products to certain states. Please check our Shipping & Return Policy before placing an order (see restrictions).

DISCLAIMER: If you are new to the world of DIY gun building, you likely have a lot of questions and rightfully so. It’s an area that has a lot of questions that, without the correct answers, could have some serious implications. At, we are by no means providing this content on our website to serve as legal advice or legal counsel. We encourage each and every builder to perform their own research around their respective State laws as well as educating themselves on the Federal laws. When performing your own research, please be sure that you are getting your information from a reliable source.

We are a national retailer of individual components and not all products depicted on this website are legal in every state. Shipping of various products found on this website are prohibited to some states (such as California, Connecticut, District of Columbia, Hawaii, New Jersey, New York, Rhode Island, and Washington). The information, pictures, text or products presented on this website are not a representation by us, and should not be understood by you, that any product or completed firearm is legal to assemble or own in your state of residence. We encourage each and every builder to perform their own research about the state and federal laws that apply to them. It is your responsibility to understand the law and we encourage you to consult with an attorney or your local ATF representative.