If you want an instant pitch on what you should buy from the market right now, then buy an AR-15 in 5.56x45mm with a 16 inch lightweight profile barrel, mid-length gas system, chrome lined barrel, and 1:7 twist from Daniel Defense, Bravo Company USA, or Spike’s Tactical.

Intro

However, if you’re here for a more in depth explanation of the AR-15 platform since you want to buy one, but all of the choices on the market are absolutely mind boggling, then stick around, because this guide is written with you in mind. This guide assumes you’re currently living within the United States when it comes to aspects of legality, however, all other engineering and technical information will be strictly correct.

History

The AR-15 rifle, invented by Eugene Stoner and having served since the Vietnam conflict of the 1960s under the US Government designation of M16, is currently one of the most reliable, rugged, and user-friendly firearms on the market. Since its introduction, there have been a number of gripes about its design, the notable one during the Vietnam War was that it would jam and render itself inoperable unless it was taken apart and cleaned out thoroughly. These problems have long since been sorted out, with the original jamming complaint isolated down to an issue with the ammunition the soldiers were issued at the time.

Since then, the platform itself has evolved with the addition of chrome lined bores, varying barrel profiles, as well as a carbine variant designated the M4 (Further developed into the M4A1). With these particular developments of the weapons platform, the back flow of variants, products, ideas, and opinions into the consumer market has exploded into a vast market of available options for the discerning consumer.

Knowing What You Want

Whether you’re looking for a new rifle to take with you on patrol or just a paper puncher, it helps to know exactly what you want to do with it. This guide won’t be pandering to any particular ideas that one caliber can do absolutely everything you would want from CQB ranges to mile-long sniper shots, but the variations of the AR-15 platform will allow a seasoned user to tailor builds and ammunition loads to hit targets from up close and personal to beyond 600 yards. The most important thing to take away from this warning is to know exactly what you want out of a semi-automatic rifle such as the AR-15 before you buy it.

Design Concepts

In knowing what you want, I prefer to separate AR-15s into a few categories: pistol, general purpose, and accuracy builds.

Pistol: You want an SBR (Short Barreled Rifle) but your local laws say you can’t have one. Next best thing is to build a shortened AR-15 that’s classified as a pistol by the ATF, so you can get the ‘shooting a tiny rifle’ experience in a sans-tax-stamp package.

General Purpose: What most people want their rifle to be/do. If you’re new to AR-15s or shooting in general, I would suggest you stick to doing this instead of immediately jumping into accurized builds or anything more niche. What this build will generally be good for is getting your shooting out to approximately 300 yards with iron sights, or beyond that if you’re good at shooting.

Accuracy Build: This is a bit of a niche sector, home to the 18+ inch barrel club, with fluted barrels and stainless steels that open up a world of hurt in terms of ballistic coefficients and barrel harmonics. If you’re building here, then you shouldn’t really need this guide since you should know what you’re doing. (To clarify, this is not a beginner’s category for an initial build. You’ll be spending a lot of time and money on something that you may not like in the end.)

Weapon Design: Upper/Lower

The AR-15 is a gas operated, magazine fed, semi-automatic rifle with a rotating bolt originally actuated via direct impingement (though that itself is somewhat of a misnomer, but that’s a different discussion for a different day), meaning that the expanding gasses from the fired cartridge are redirected back at the bolt to make it cycle.

The major components of the rifle can be separated along a major line into the upper and lower receiver groups. Inside the United States, the only part of the system that is considered the firearm (serialized and regulated) is the lower receiver. Attached and within the lower receiver, you have the stock, buffer system, pistol grip, and trigger group. Attached to the upper receiver, one will normally find the barrel, hand guard, front and rear sights, as well as possibly a forward assist. Any other attachments that may end up on a rifle, such as a bipod, laser aiming system, or optics will be solely on purpose and user preference.

Caliber Introduction

Originally designed for the 5.56x45mm caliber that revolutionized combat theory in the modern age, the AR-15 platform has since evolved into other roles, taking on the ability to use anything from .22 Long Rifle to .50 Beowulf. This particular modularity brings about choices for the consumer that will likely be very confusing at first glance.

For the beginner, I recommend simply sticking to what it was designed for and buying a rifle in 5.56x45mm. This will not only save you the hassle of finding specialized upper receivers in the caliber you want, but it will also allow you to get more bang for your buck when it comes to ammunition. However, if you simply must buy a rifle in a different caliber (due to local laws or even budgetary concerns), I will go over some of the available alternative calibers below.

.22LR (Long Rifle) : This venerable varminting and target shooting caliber will give you the cheapest shooting experience for your money. Since this is a rim fire cartridge, the prices will be much lower in comparison to any center fire alternatives. However, also because this is a rim fire cartridge, any malfunctions that occur in your rifle because of ammunition will be much, much harder to fix.

: This venerable varminting and target shooting caliber will give you the cheapest shooting experience for your money. Since this is a rim fire cartridge, the prices will be much lower in comparison to any center fire alternatives. However, also because this is a rim fire cartridge, any malfunctions that occur in your rifle because of ammunition will be much, much harder to fix. 9x19mm Luger/Parabellum : This NATO standard cartridge does well in the AR-15 platform, transforming it into a technical submachine gun rather than a rifle platform. This is probably the most prolific alternative caliber for shorter barreled AR-15s on the market and will provide you the same enjoyable shooting for less than you would need to spend on 5.56.

: This NATO standard cartridge does well in the AR-15 platform, transforming it into a technical submachine gun rather than a rifle platform. This is probably the most prolific alternative caliber for shorter barreled AR-15s on the market and will provide you the same enjoyable shooting for less than you would need to spend on 5.56. .45ACP : A very American caliber that is older than the AR-15 platform, the .45ACP cartridge provides an alternative pistol caliber for the discerning shooter. However, I cannot personally recommend this decision based on the relative prices of the ammunition between this and mil-spec 5.56 being so close to each other.

: A very American caliber that is older than the AR-15 platform, the .45ACP cartridge provides an alternative pistol caliber for the discerning shooter. However, I cannot personally recommend this decision based on the relative prices of the ammunition between this and mil-spec 5.56 being so close to each other. .223 Remington/5.56x45mm : The important note to make here is that .223 is NOT the same as 5.56 caliber. Sparing the details, a rifle chambered in 5.56 is compatible with .223 ammunition, but not the other way around. .223 is a perfectly fine caliber used for hunting small and medium sized game where local laws allow, and is priced similarly to its military standard brother. 5.56 operates at a higher pressure than .223 with a different (looser) headspacing to allow for a much wider selection of ammunition to be used.

: The important note to make here is that .223 is NOT the same as 5.56 caliber. Sparing the details, a rifle chambered in 5.56 is compatible with .223 ammunition, but not the other way around. .223 is a perfectly fine caliber used for hunting small and medium sized game where local laws allow, and is priced similarly to its military standard brother. 5.56 operates at a higher pressure than .223 with a different (looser) headspacing to allow for a much wider selection of ammunition to be used. .223 Wylde : This is a proprietary chambering which addresses the pitfalls of the .223 Remington versus 5.56x45mm compatibility issues. This, and other ‘hybrid’ chamberings, are proprietary, and generally will market themselves as being able to shoot both .223 and 5.56 ammunition equally well. This is a good thing to look out for if you’re building a general purpose rifle.

: This is a proprietary chambering which addresses the pitfalls of the .223 Remington versus 5.56x45mm compatibility issues. This, and other ‘hybrid’ chamberings, are proprietary, and generally will market themselves as being able to shoot both .223 and 5.56 ammunition equally well. This is a good thing to look out for if you’re building a general purpose rifle. .300 AAC Blackout : A relatively new caliber to the market at the time of writing, this cartridge was designed to bring the punch of a 7.62x39mm cartridge to the platform as well as improving performance through a suppressor while still maintaining the general brass size and setup of most of the other 5.56 parts. However, expect to pay extra for the novelty.

: A relatively new caliber to the market at the time of writing, this cartridge was designed to bring the punch of a 7.62x39mm cartridge to the platform as well as improving performance through a suppressor while still maintaining the general brass size and setup of most of the other 5.56 parts. However, expect to pay extra for the novelty. 5.45x39mm : The newer Russian standard cartridge that earned a name for itself during the Russian invasion of Afghanistan, this cartridge provides a decently performing round for a lower price when using Russian surplus ammunition.

: The newer Russian standard cartridge that earned a name for itself during the Russian invasion of Afghanistan, this cartridge provides a decently performing round for a lower price when using Russian surplus ammunition. 6.8mm Remington SPC : A cartridge designed to perform better than 5.56 from a 14.5” M4 carbine barrel, it offers better terminal ballistics and 44% more energy transferred downrange, but at a much higher price.

: A cartridge designed to perform better than 5.56 from a 14.5” M4 carbine barrel, it offers better terminal ballistics and 44% more energy transferred downrange, but at a much higher price. 6.5 Grendel : A recently SAAMI standardized cartridge; it offers a middle ground between 5.56 and 7.62x51mm, with a flatter trajectory and greater terminal energy than 5.56. Furthermore, with certain setups it offers sub-MOA performance at 600 yards and out. Unfortunately, it is also relatively expensive.

: A recently SAAMI standardized cartridge; it offers a middle ground between 5.56 and 7.62x51mm, with a flatter trajectory and greater terminal energy than 5.56. Furthermore, with certain setups it offers sub-MOA performance at 600 yards and out. Unfortunately, it is also relatively expensive. 7.62x39mm : A time tested cartridge of the Soviet Union and insurgent militias, this round is now currently being offered by a number of different manufacturers in their rifles, and may offer a decent alternative to others in the AR market. The round can also be found cheaper than 5.56 as a surplus round, but be aware there have been many documented cases of AR-15s having reliability issues with 7.62x39mm.

: A time tested cartridge of the Soviet Union and insurgent militias, this round is now currently being offered by a number of different manufacturers in their rifles, and may offer a decent alternative to others in the AR market. The round can also be found cheaper than 5.56 as a surplus round, but be aware there have been many documented cases of AR-15s having reliability issues with 7.62x39mm. 7.62x51mm : This isn’t actually an AR-15 caliber; instead it belongs to the AR-15’s predecessor, the AR-10. If this is the caliber you want, this is not the guide you need, as there isn’t the same level of compatibility between AR-10 parts as there is with an AR-15.

: This isn’t actually an AR-15 caliber; instead it belongs to the AR-15’s predecessor, the AR-10. If this is the caliber you want, this is not the guide you need, as there isn’t the same level of compatibility between AR-10 parts as there is with an AR-15. .50 Beowulf: This cartridge is good for interdicting engine blocks, solid walls, and heavy targets where a 12 gauge slug would be a good option. This cartridge in particular approximately emulates the performance of .45-70 Government in terminal ballistics and has found a certain niche in both the tactical world and the hunting community. As one would expect, it is not a cheap caliber.

Barrel Profile, Material, and Length

Since the invention of the AR-15 platform, the overall contour of the barrel has been offered in a variety of sizes for different purposes. Speaking here, unless otherwise referenced for the M4 platform (14.5 inch long barrel), the standards will be for a 20 inch long barrel.

Lightweight : The lightweight profile was originally adopted with the M16A1, allowing for a very light and maneuverable gun. The look of the profile is thin all the way along the length of the barrel. In military applications, it became inappropriate since it would quickly warp under the heat of constant (read: full-auto) firing. On the other hand, this barrel profile has found widespread adoption in the civilian shooting community for its weight savings and negligible performance difference.

: The lightweight profile was originally adopted with the M16A1, allowing for a very light and maneuverable gun. The look of the profile is thin all the way along the length of the barrel. In military applications, it became inappropriate since it would quickly warp under the heat of constant (read: full-auto) firing. On the other hand, this barrel profile has found widespread adoption in the civilian shooting community for its weight savings and negligible performance difference. Government : The current standard profile for service rifles, the shorter M4 style incorporates a notch forward of the gas block to allow for mounting of the M203 40mm grenade launcher while the 20″ length profile is simply thinner underneath the hand guard with a significantly thicker portion forward of the gas block.

: The current standard profile for service rifles, the shorter M4 style incorporates a notch forward of the gas block to allow for mounting of the M203 40mm grenade launcher while the 20″ length profile is simply thinner underneath the hand guard with a significantly thicker portion forward of the gas block. HBAR : The HBAR profile finds its home in long distance shooting and hunting, with a very thick barrel all the way along to the end. This is not to be confused with the bull barrel.

: The HBAR profile finds its home in long distance shooting and hunting, with a very thick barrel all the way along to the end. This is not to be confused with the bull barrel. Bull : A thicker profile than the HBAR, a bull barrel will perform a bit better in grouping sizes than its thinner counterpart.

: A thicker profile than the HBAR, a bull barrel will perform a bit better in grouping sizes than its thinner counterpart. SPR: The SPR profile was developed in recent years with the Mk12 SPR (Special Purpose Rifle) program. This profile is ‘supposed’ to be at an 18” barrel length, with thickness running past the front sight, but tapering slightly after it as well as allowing for threading at the end of the barrel for a muzzle device.

Along with different barrel profiles, a savvy consumer has to worry about the barrel length. This ties back to the initial point of knowing what you want. 5.56x45mm was originally designed with a 20 inch barrel in mind, using a 12 inch gas system: this setup is ideal since it allows for much lower pressures in the action, higher velocities, and a longer sight radius if an A2 style front sight is being utilized. Furthermore, on most military standard ammunition, velocities at or above approximately 2700 fps are essential to terminal fragmentation of the round, something which the shorter carbines do not always reliably achieve. Eschewing any in-depth discussion of barrel length interaction with different gas lengths, popular barrel lengths include:

20 inches : the old standard for the AR-15 platform, this provides maximum velocity for any cartridge. In the right profiles and twist, this length will do just as well as a regular battle rifle and a precision build.

: the old standard for the AR-15 platform, this provides maximum velocity for any cartridge. In the right profiles and twist, this length will do just as well as a regular battle rifle and a precision build. 18 inches : A popular hunting and marksmanship length of barrel in certain profiles and twists. This is also the minimum length of barrel commonly available that will function with a rifle length (12 inch) gas system.

: A popular hunting and marksmanship length of barrel in certain profiles and twists. This is also the minimum length of barrel commonly available that will function with a rifle length (12 inch) gas system. 16 inches : This is the US Federal minimum length for a rifled barrel without being classified as a short barreled rifle. Good balance of modularity and compactness for the average civilian owner.

: This is the US Federal minimum length for a rifled barrel without being classified as a short barreled rifle. Good balance of modularity and compactness for the average civilian owner. 14.5 inches : The standard M4 Carbine length barrel delivers workable performance from a much smaller package than the M16. For civilian ownership without a tax stamp, this length will require a pinned and welded muzzle device that makes it meet the 16” federal standard.

: The standard M4 Carbine length barrel delivers workable performance from a much smaller package than the M16. For civilian ownership without a tax stamp, this length will require a pinned and welded muzzle device that makes it meet the 16” federal standard. 10.3 inches : The standard length for a MK18 CQBR rifle, this is normally used for ‘pistol’ designated AR-15s or registered short barreled rifles.

: The standard length for a MK18 CQBR rifle, this is normally used for ‘pistol’ designated AR-15s or registered short barreled rifles. 10/10.5 inches : Another short barrel length one may find on the market that is good for pistol type guns.

: Another short barrel length one may find on the market that is good for pistol type guns. 7 inches: The shortest common barrel length one may find on a given AR-15 pistol. This will be the loudest and flashiest of any of the barrel lengths, since it doesn’t have the length to allow all of the powder to burn up before the projectile leaves the barrel.

The other consideration available for the end user is the actual metal the barrel is created from. There are generally three types of barrels currently on the market: milspec, non-milspec, and stainless steel.

Milspec : This simply means the barrel meets the military specification of durability and longevity. Generally for a civilian consumer, if it meets the military’s specifications, it is probably a good choice.

: This simply means the barrel meets the military specification of durability and longevity. Generally for a civilian consumer, if it meets the military’s specifications, it is probably a good choice. Non-Milspec : These barrels do not meet military standard specifications and do not demand equivalent pricing since they may have lower pressure or heat tolerances. However, if your usage is not going to involve firing thousands of rounds through your barrel in one sitting, you may never know the difference.

: These barrels do not meet military standard specifications and do not demand equivalent pricing since they may have lower pressure or heat tolerances. However, if your usage is not going to involve firing thousands of rounds through your barrel in one sitting, you may never know the difference. Stainless Steel: This particular type is popular on accuracy oriented builds. Durable in its own right, an equivalent stainless steel barrel is 2% heavier than its carbon counterpart and will typically come in a heavier profile than their standard steel counterparts. These also cannot be chrome lined, nor are they as heat resistant, so extended rapid fire should usually not be in this type of barrel’s normal use.

Twist

Barrel twist is the distance a bullet needs to travel in order complete one full rotation, so a 1:10 (read “One in Ten”) twist would be one full revolution every 10 inches. The internal twist rate of the barrel has changed with the development of the 5.56×45 cartridge, with the original M16 prototypes sporting a 1:14 twist. All twist comparisons below are meant only for reference in using 5.56×45.

1:7 : The current US military standard twist rate, it performs well, stabilizes a wide variety of ammunition, and in general will perform well enough for most end users using 50-80 grain ammunition.

: The current US military standard twist rate, it performs well, stabilizes a wide variety of ammunition, and in general will perform well enough for most end users using 50-80 grain ammunition. 1:8 : A relatively new twist rate at the time of this writing, it is designed to bridge the gap between 1:7 and 1:9 twist (obviously). However, a number of manufacturers do not make a ‘true’ 1:8, instead rounding up from 1:78 or thereabouts. I personally recommend 1:8 twist if you can find it, since it provides better performance from a wider variety of bullet weights without making some of the sacrifices 1:9+ will.

: A relatively new twist rate at the time of this writing, it is designed to bridge the gap between 1:7 and 1:9 twist (obviously). However, a number of manufacturers do not make a ‘true’ 1:8, instead rounding up from 1:78 or thereabouts. I personally recommend 1:8 twist if you can find it, since it provides better performance from a wider variety of bullet weights without making some of the sacrifices 1:9+ will. 1:9 : An older twist rate popular with the hunting and target shooting community after the decline of the .222 Remington cartridge which 5.56x45mm is based off of, this one will provide support for a wide variety of cartridges, but lacks some of the range 1:8 provides.

: An older twist rate popular with the hunting and target shooting community after the decline of the .222 Remington cartridge which 5.56x45mm is based off of, this one will provide support for a wide variety of cartridges, but lacks some of the range 1:8 provides. 1:12 : The early M16 twist rate that has fallen out of style. This twist is meant for 55 grain or lighter bullet weights.

Chrome Lining

To prevent corrosive ammunition from quickly eating away at the barrels when left unmaintained, manufacturers use a chrome lining on the inside of the barrel. This has a number of advantages as well as disadvantages depending on the purpose of the rifle. Choosing a barrel with a chrome lining opens up the market for a consumer, since a large majority of quality manufacturers these days are vying to make military type barrels, and aside from the added durability in maintenance, a chrome lining will extend a barrel’s round count lifetime.

The disadvantages of chrome lining treatment however include a possible reduction in accuracy. This does not mean a significant difference in accuracy for the shooter unless one is using the rifle for extreme accuracy in target shooting and will most likely go unnoticed by the average consumer.

Gas System / Piston

Originally, the AR-15’s recoil system was designed on the idea of direct impingement, where the hot gasses of an expended cartridge leaving the barrel are partially redirected back at the bolt carrier, causing the action to cycle. In recent times, a new pattern has become popular that utilizes a short stroke piston, using that to move the bolt and cycle the action while also venting hot gasses at the gas block. The only noticeable advantage in this new system is that the carbon buildup that would normally flow back into the action is now at the gas block, and hot gasses are vented there, leaving the bolt cool to the touch immediately after firing. I cannot recommend a piston system on a civilian AR-15 platform for sheer pragmatism; it does not provide enough advantages over the direct impingement system of the AR-15 platform to outweigh the adoption costs.

Direct impingement brings on a whole host of other issues, with the need to account for different pressures in chamber and gas port hole sizes. A good rule of thumb for optimal barrel length is “gas length plus 5 inches”. By and large, this is all fairly standardized and the AR-15 gas length offerings on the market will be one of the following:

Pistol (4 inch) : This is the shortest gas length system on the market, and will cause the most wear and tear on your action because of its high pressures. This gas length is probably only truly appropriate for barrels between 7 and 9 inches.

: This is the shortest gas length system on the market, and will cause the most wear and tear on your action because of its high pressures. This gas length is probably only truly appropriate for barrels between 7 and 9 inches. Carbine (7 inch) : The current military standard for the M4 Carbine and the Mk18 CQBR, this gas length provides workable, but not ideal, pressure and dwell time for AR-15 platforms. The felt recoil will be a bit harsher, and the wear on the action will be a bit more than longer alternatives. This gas length will work best for barrels between 10 to 16 inches.

: The current military standard for the M4 Carbine and the Mk18 CQBR, this gas length provides workable, but not ideal, pressure and dwell time for AR-15 platforms. The felt recoil will be a bit harsher, and the wear on the action will be a bit more than longer alternatives. This gas length will work best for barrels between 10 to 16 inches. Midlength (9 inch) : A relatively recent development in the AR-15 world, this gas length gives the best balance for 14-16” barrels. With a softer felt recoil while maintaining operational reliability, this is definitely a length the author would recommend over the traditional carbine length.

: A relatively recent development in the AR-15 world, this gas length gives the best balance for 14-16” barrels. With a softer felt recoil while maintaining operational reliability, this is definitely a length the author would recommend over the traditional carbine length. Intermediate (10-11 inch) : A mostly proprietary gas length, Noveske in particular uses this gas port distance on their 18” rifles.

: A mostly proprietary gas length, Noveske in particular uses this gas port distance on their 18” rifles. Rifle (12 inch): The traditional gas length that came with the original AR-15 and stays strong and true in the M16 series, this provides the softest felt recoil due to its low pressures (because of the distance from the chamber), and will cause the least amount of wear and tear to the action.

The Upper Receiver

The upper receiver itself is simply a hunk of metal that the barrel needs to be screwed into to properly chamber a round in the functioning of the weapon. This description, however, does not mean that the upper is a low impact part. The whole of the upper receiver is the higher impact half of the AR-15 system, since that is where the explosions happen when the cartridges are ignited and hot gasses are vented down the barrel. The two types of receiver made commonly on the market are forged and billet: between the two it doesn’t make much of a difference to the end user and both will perform well under normal circumstances.

A ‘Billet’ receiver means that it was carved out of a single contiguous block of aluminum, allowing for variations from the standard AR-15 upper design. A single passing advantage of the billet make is that it has the potential for tighter tolerances than its forged counterpart, which may be beneficial to a precision oriented build.

A ‘Forged’ receiver, as its name implies, is a receiver made from forged aluminum. In general, forging will produce a consistently stronger product than its billet counterpart.

The Forward Assist

The part of the AR-15 that has probably received the most chagrin in the whole design is the forward assist. Originally ordered as part of the Army’s M16A1 (in contrast to the Air Force Security order for the true original AR-15 series without a forward assist), the actual use for this particular part of the gun is to force the bolt to close home from an out of battery state. With any experience in the field or even at the bench, a majority of modern shooters have never had to use their forward assists and many shooting instructors will recommend against ever using it since it has the propensity to catastrophically jam a problem that may need a different type of attention than forcing the bolt shut.

As a civilian consumer, this is not the most ‘necessary’ of parts, however a majority of reputable manufacturers will continue making their upper receivers with a forward assist. Aside from one model of the Smith and Wesson M&P 15 which lacks the forward assist and dustcover, to have a rifle without it on the upper receiver, you’ll have to hunt down a custom manufactured upper receiver that does not have it built into the metal (Rainier Arms, VLTOR, Les Baer).

Bolt Carrier Group

The bolt carrier group (BCG) is arguably the most important part of the rifle. This is the part that will be taking most of the hammering when it comes to action, and comes in a number of flavors, but only one of them really matters. I generally recommend using an M16/Full Auto bolt carrier group for both market availability and ease of parts replacement as well as proper functioning.

The M16 or Full Auto bolt carrier group, comes with a fully shrouded firing pin and no material removed from the bottom portion, which makes it the heaviest of the types available.

The AR-15 bolt carrier group has a significant amount of material shaved off of the rear of the unit, mostly as a corporate ‘safety precaution’ to prevent it from being used in a fully automatic configuration. This removed material leaves the firing pin open and lightens the weight of the unit, which may cause problems for extraction and timing.

The AR-15 enhanced bolt carrier group is a blend of the above two, with only a small amount of material removed from the body of the carrier group to prevent it from being used in a fully automatic configuration. These generally will serve you no better than an M16 BCG.

The mark of a good bolt carrier group comes in its testing, the most common of these being a High Pressure Test, Magnetic Particle Test, Shot Peening, and Gas Key Staking.

High Pressure Tested means that the part has been checked to make sure that it is within the design parameters for pressure exerted on the part.

Magnetic Particle Tested means the part has been placed under magnetization and checked for irregularities below the surface.

Shot Peening is a mechanical process that improves the durability of the part.

Gas Key Staking is indenting the metal around the screws that go on top of bolt carrier group to prevent them from backing out. This is not entirely necessary in the function of the AR-15; however it is a nice touch of preventative maintenance. A properly staked gas key is normally a sign of a good manufacturer.

Some of the companies which meet these mil-spec standards for bolt carrier groups are Daniel Defense, Colt, Bravo Company USA, Lewis Machine & Tool, and Spike’s Tactical.

Muzzle Devices

Muzzle devices can be divided generally into three camps: Flash Hiders, Muzzle Brakes, and intermediate devices.

Flash Hiders, as their name implies, are meant to reduce/eliminate the flash signature of the rifle from the ignition of unburned powder after leaving the barrel. These will normally come in two flavors: Pronged and birdcage. The pronged variety are like tuning forks which will ring distinctively with each shot whereas the birdcage varieties will be more muted in their tone.

Muzzle Brakes are designed to reduce muzzle jump by venting the gasses in a meaningful direction (Usually the 180 degrees ‘upward’ from the rifle). Because of the way these are designed, most will also cause annoyance to anyone directly to the side of the shooter, since every shot will emit a concussive wave. These devices also normally have little to no flash suppressing properties, so during low-light and night conditions both shooter and observer will see a distinct muzzle flash.

Intermediate devices cover a broad range of ‘other’ products on the market that claim to do a little bit of both in terms of flash suppression and muzzle braking. However, do not expect them to excel at both of these characteristics at the same time; the majority of these products will only be passable at either function.

Furniture (Stock, Grip, Hand Guard)

The parts the user interacts with and rests on are generally the stock, grip, and hand guard. As a whole, these are referred to as the AR’s ‘furniture’.

Stock – Fixed vs Collapsible

Stocks generally come in two types: fixed or collapsible. Before getting into what exactly that means for you, there are two terms that need to be discussed: the overall length of the stock, which is self-explanatory, and the ‘length of pull’(LOP). The LOP is the distance between the end of the stock to the front face of the trigger. This becomes important in measuring your own length of pull (distance from elbow to bent forefinger) to make sure that you’ll be comfortable shooting the particular stock design you want. The total length of a fixed stock will be longer than a fully collapsed adjustable stock. As a general rule, I recommend a collapsible stock to everyone unless you want a stability oriented precision-build since it will be more modular and allow you to find your preferred length of pull and setup.

The standard US military fixed stock is the A2 stock, and is referenced as such in most literature. This is the baseline standard of modern stocks with an overall length of 10.5 inches, and a length of pull of 13.5 inches. Otherwise, if you want a fixed stock, there are other variants shorter than the A2 stock marked as ‘entry’ or ‘stubby’ stocks, which emulate a fully collapsed adjustable stock. Other than the military style, companies such as VLTOR, Magpul, Rock River Arms, and ACE have some decent fixed stock options.

The standard US military collapsible stock is a Colt collapsible stock, which by all means is not the best stock on the market for features. A technicality before dealing with collapsible stocks is that there are two different types of carbine buffer systems that are on the market today: milspec and commercial. The key difference is that the commercial spec tube has a slightly larger outer diameter that forces you to buy commercial spec stocks. I cannot recommend this, as milspec provides a larger pool of options to choose from. There are a plethora of collapsible stocks available on the market today, with major name brands such as Magpul, LMT, VLTOR, ACE and many others producing quality products that will give you a maelstrom of choices.

Grip – Options Other Than A2

The standard pistol grip for the AR-15 that normally comes prepackaged in lower parts kits for builders is the A2 pistol grip. In the author’s opinion it is uncomfortable, cheaply made, and not worth its own weight in plastic. However, if cost is an issue, the A2 grip will work, and you can sometimes find it being given away for free since people rarely want it. As with collapsible stocks, there are innumerable variations available on the market today from major companies, and one would do well to replace the A2 grip if it is uncomfortable.

Hand Guard – Freefloating vs Non-Freefloating

The hand guard or fore-end of the rifle is the part that covers up the gas tube between the receiver and the front sight. This usually comes in two flavors: non-free-floating or free-floating. What this means is that some hand guard designs use a proprietary system to make sure that the hand guard makes no contact with the barrel, allowing for less interference on the whole of the rifle. The advantages of having a free-floated hand guard are that the barrel will have significantly fewer points of contact from outside forces and as such will be much less subject to any tension being put on the hand guard (Sling, grip positions, pressure, etc). The disadvantages to a free-floating system are that you will have to deal with a proprietary barrel nut (if installing aftermarket, you need a specialized setup for this), and of course figuring out which rail system you want the most, since these tend to be a semi-permanent decision if you don’t have the equipment to add or remove them.

It is this author’s opinion that there are enough merits to using a free-floating rail system that make it a superior choice in this particular matter.

Sights (Fixed vs Folding)

Rifle sights come in two different formats: fixed or folding. Before any discussion, it is generally noted that the longer sight radius (distance between rear and front sight), the better it is for accuracy. Fixed sights are standard on military issue rifles, with the rear sight integrated into a carry handle attachment and the front sight being part of the gas block. Overall, what this provides is a very stable and very durable sight platform that will perform exactly as advertised without many frills.

Folding sights tend to be more modular than fixed sights, with the rear assembly allowing for different shapes and sizes of rear aperture and the front becoming an entirely new system. Both front and rear folding sights sometimes also come with a spring assisted deployment. Folding front sights offer the ability to have them mounted onto the hand guard of the rifle instead of being integrated with the gas block, thereby allowing a longer length hand guard to be used in conjunction with a low profile gas block, giving the user the option of a longer sight radius, or even mounting a flashlight in front of the front sight. Other variants of folding front sights are integrated with the gas block, which allows the user to put the sight out of the way of an optic in case one is mounted, drawing a mid-line between a rail mounted sight and a gas block integrated sight.

Of note are the dimensions folding sights will come in, with variations ranging from gas block height, rail height, and ‘micro’ sized sights. The gas block height front sights are taller than the ‘standard’ rail height front sights to allow them to be mounted on a railed gas block instead of the front of a free floated hand guard. Rail height sights are the most ubiquitous variety, matching the rail atop the upper receiver and the hand guard. Micro sized sights are shorter in height, meant to match up to particular rail heights of other rifle series such as the SIG 550, HK 416, or SCAR rifles, generally there won’t be a reason to even consider this height if you’re dealing with market standard AR 15 parts.

My personal recommendation on this is to buy a set of metal, non-spring assisted folding sights and mount them to the rear of the upper receiver and as far forward on a free float rail as possible. This is for a number of reasons; chiefly I recommend metal sights (at least for the front sight) since certain polymer back up sights that are on the market have a tendency to melt if mounted on the gas block.

Trigger (Single Stage vs Two Stage; Aftermarket Options)

The default trigger system in mil-spec rifles is a single stage trigger. What will come in the standard build lower parts kit will be a mil-spec style single stage trigger. This will generally be a fairly heavy trigger pull for a heavy snap feeling break. While it works and is good enough for most general purpose rifles, many shooters decide to upgrade to a two-stage trigger later.

A vast majority of aftermarket triggers are two-stage triggers, changing the trigger pull feel to some amount of no-effort take-up to a light, crisp break. The two largest names in the AR-15 aftermarket trigger industry are Geissele and Timney, however there are other brands out there producing their own triggers such as Rock River Arms and Spike’s Tactical.

My recommendation for a good trigger upgrade is to wait until you know how you shoot and the way you want to shoot before throwing your lot in with any particular trigger system. Many companies make specific triggers for combat, precision shooting, 3-gun competition shooting, etc. Working with a mil-spec single stage at the first part of your AR-15 ownership will provide you with valuable experience before being pampered by a two stage system.

Extras (KNS anti-rotation pins, etc)

Of course, as the nickname goes, the AR-15 is ‘Barbie for men’ with more accessories than you can shake a stick at. These little gizmos and doodads range from anti-rotation pins in the receiver to accurizing wedges in the lower receiver or even cant mounts for putting alternative 45 degree angle sights on your rifle. I won’t be recommending anything in particular in this section, but it is worthwhile to note that a beginner level consumer should probably look around before committing to any single particular set of extra gadgets that may be unnecessary to their shooting style.

DIY vs Pre-Assembled

Having finished with all of that, the remaining question is “Do I buy a rifle that’s already been fully assembled, or do I try and build one for myself?” There are distinct advantages to a pre-assembled rifle, with the most recent one being a cheaper overall price tag. Recently many companies have pushed down their prices for buying complete rifles from them, which gives an additional level of warranty service over simple individual part guarantees. With a complete rifle, if your rifle doesn’t function as advertised or experiences some severe failure, the company will normally have it sent back to them and they’ll fix it for you, unlike a self-built rifle which will require the attention of an experienced gunsmith if the system as a whole does not function properly even when the individual parts are fine.

However, building your own rifle also has its advantages. If you decide to build your own AR-15, starting with a stripped lower receiver, you can make it exactly the way you want it, tuning everything down to the type of detents and buffer weights you want to start out with. The downside of all of this lies in building the upper receiver assembly, which will require a vice and specialized tools needed to deal with the AR-15. The level of modularity available to the AR-15 platform in the consumer market lends to a very personal build, allowing you to satisfy what you want in the gun instead of languishing over what-could-have-beens and selling the gun later as a result of this disappointment.

To split the difference, it is also perfectly viable to build a complete upper receiver or complete lower receiver and then just buy a pre-built assembly from a major manufacturer and put the two together. The only warning I have here, again, is that the upper receiver takes more effort and a few more tools to build than the lower receiver does, and this is a major stopping point for most people.

My personal recommendation on this matter is to build a lower receiver on your own and customize it to how you want it and then buy a pre-built upper receiver. Most of the hard work will be done for you, allowing you to customize your gun to how you like it from there.

US Rifle vs Pistol Designation

Particular to US law, you can buy AR-15 lower receivers designated for either a pistol or a rifle. The rifle option is fairly straightforward; you can put a stock on it and throw any upper receiver with a 16” or longer barrel on it with no repercussions or extra paperwork. However, if you want a barrel shorter than 16 inches, you have to be in a state which allows Short Barreled Rifles for civilians and will have to fill out a form and pay for a tax stamp for the SBR.

The pistol designation goes the other way, it may never have a stock or vertical fore-grip attached to it, although you can use whatever length upper receiver you feel since it is considered a long barreled pistol.

Author and Editor Opinion (The Round-Up)

To reiterate my opinion, if this is your first AR-15 (or even first semi-automatic long arm) I would recommend you buy a complete rifle with a 16” barrel (for modularity of the muzzle device) with a 1:7 twist, chrome lined barrel, mid-length gas system (and therefore a 9”+ rail) in 5.56x45mm from a major manufacturer (I happen to like Daniel Defense). What other accessories or furniture you decide to install on it can be cultivated over time (for a lot less than what it would cost to change barrels and upper receivers). From there I would recommend 3 or 4 times the amount spent on the whole rifle be spent on ammunition to go out and practice shooting it since that’s what will make you successful.

However if this is not your first rodeo, I would recommend building your own AR-15 from a stripped lower receiver and buying a complete upper receiver to match the purpose that you’re looking to shoot the gun in.

I’ve avoided discussing any form of optics for sake of brevity, that would require another guide unto itself to really explore even a beginner’s set. Learn to shoot with iron sights first before you rely on glass.