AR-10 vs AR-15 vs AR-9: Here’s how to spot the difference

Since the end of the 2004 Assault Weapon Ban, the AR platform has exploded in popularity. For someone new to firearms, it may seem like there are too many black rifles that look very much the same. This guide is to help you understand the differences and similarities that they have, as well as some knowledge I’ve accumulated since I bought my first AR over 20 years ago.

The most popular versions of these sporting rifles are the AR-15, AR-10, and AR-9. While more variants exist, the bulk of the AR-pattern rifles will fall under these three types. Each has its own best use scenario, and each is meant to shoot different cartridges.

The AR-15, which is an acronym for “super bad Assault Rifle and don’t you ever say otherwise”, was the predecessor to the M16. It was modified and adopted as the service rifle meant to replace the M14 during the Vietnam war. But, its acceptance by the civilian market will ensure that it stays relevant far beyond its inevitable replacement by the military.

History Lessons

In the Post-WWII era, the U.S. Military was looking for a rifle to replace the M1 Garand with something lighter, smaller, and higher capacity.

In the 1950s, a firearms engineer by the name of Eugene Stoner led a team that developed the AR-10. It was chambered in 7.62x51mm, used a 20-round detachable box magazine, and utilized aluminum and plastic in key parts to reduce its overall weight.

The company Stoner worked for, ArmaLite, submitted this rifle design to Springfield Armory (no relation to the current firearms company of the same name) for testing and evaluation. The design was not adopted and during the testing, one of the supplied models had a catastrophic barrel failure.

Ultimately the M14 was selected to replace the M1 Garand and the AR-10 largely faded into obscurity.

The AR-15 was developed as a downsized version of the AR-10, originally chambered in 222 Remington, but more famously chambered in the more powerful 223 Remington. Both designs were ultimately sold to Colt’s Manufacturing Company (universally referred to as just “Colt”).

It was under the ownership of Colt that the AR-15 would gain the attention of the United States Air Force and subsequently be adopted as the M16, going on to be widely issued during the Vietnam war.

The Modern Era

In the civilian market, the AR family of rifles exploded in popularity in the early 2000s. The Clinton-era Assault Weapons Ban (AWB) expired in 2004 and, as can happen, outlawing a certain thing ultimately makes it more popular.

The AR-15, which was only made by a handful of companies at the start of the AWB, exploded in popularity to become the defacto standard semi-automatic rifle in the U.S. market. The popularity of the AR-15 pulled the AR-10 back out of obscurity and eventually led to the creation of the AR-9.

Now that the backstory behind the AR family of rifles has been briefly explained, I will entirely focus on how each of these rifle platforms exists in its current form.

Characteristics of the AR-15

For illustrative purposes only, please do not use the American flag as a gun mat.

The AR-15 is often referred to as a family of rifles in and of itself. This is because the modern AR-15 can be chambered in more than a dozen cartridges, can be assembled using parts from a dozen companies, and those parts rarely need any fitting or gunsmithing to make a functional rifle.

The most unifying factor among all the different makes and models is that the cartridges are limited to an overall length of 2.260 inches. Once a cartridge goes much over this length, it will no longer fit into an AR-15 pattern magazine.

Even with this limitation, manufacturers have created cartridges ranging from the speed-demon .204 Ruger to heavy-hitting .458 SOCOM. This gives the AR-15 the ability to be tailored to the needs of the shooter better than any other semi-automatic rifle in existence.

And because the critical step of measuring barrel headspace is done at the factory, the end-user can swap out a barrel with simple tools. The barrel wrench I have used to replace two barrels on my competition AR-15, and to build several rifles for friends, cost me only $30.

Another amazing aspect of the AR-15 is that virtually all of the parts made by various companies are compatible with each other. The glaring exception to this rule is parts meant for a piston-operated AR-15. Thankfully, these are becoming less and less popular as time goes on.

If a friend called me tomorrow and said they had a lower receiver made by one company, a parts kit from a second company, and a drop-in trigger from a third company, I could assemble it for him with zero fitting or modifications.

Generally, the end-user just needs to select the proper combination of parts for a certain cartridge to have a functional rifle. Some cartridges, such as the .300 Blackout, require as little as a new barrel and muzzle device to be functional with all other parts meant for a “standard” AR-15 chambered in 5.56x45mm.

Most cartridges though require a couple of parts more to be replaced.

The golden standard of chamberings for the AR-15 is still 5.56x45mm. That, or a .223 Wylde chambering, will allow for the usage of any standard .223 Remington or 5.56x45mm ammunition. If an AR-15 is chambered in .223 Remington it is not recommended to shoot 5.56x45mm ammunition out of it, as pressures can reach unsafe levels.

When newer shooters approach me with ideas of buying (or building) an AR-15 in a less common cartridge, such as 6.5mm Grendel or .450 Bushmaster, I always try to steer them back toward 5.56x45mm. The price to performance ratio of .223 Remington and 5.56x45mm ammunition cannot be beaten.

I don’t recommend straying from the golden standard until a shooter already owns an AR-15 in 5.56x45mm and has the financial means to practice with it regularly.

Because of the limit on the overall length of a cartridge, the AR-15 needs to compromise between range and hitting power. Small caliber bullets can stretch out the usable range of the AR-15, while large caliber bullets can make the AR-15 viable for hunting dangerous North American game at close distances.

The 6.5 Grendel has become the most popular combination of hitting power and usable range, but even it isn’t considered a “full power” rifle cartridge.

Characteristics of the AR-10

If an AR-10 were transformed into a man, that man would be a Viking.

The AR-10 is the literal “big brother” of the AR-15, but it has some distinct drawbacks that need to be understood.

The AR-10 can be chambered in several cartridges but has nowhere near the selection available to the AR-15. The common theme with the cartridges available to the AR-10 is that they can have a maximum overall length of approximately 2.85 inches.

Once again, a cartridge needs to feed from a detachable box magazine to be useful in the AR platform.

Factory-produced AR-10 rifles are largely chambered in one of two cartridges, the .308 Winchester and the 6.5 Creedmoor. Less common chamberings include the .243 Winchester, 6mm Creedmoor, 7mm-08 Remington, and the .22-250 Remington.

Compared to the AR-15, the AR-10 will always have more hitting power, more range, or both. There is no reason for an AR-10 to exist if it doesn’t do at least one thing better than the AR-15.

The drawbacks of the AR-10 are two-fold; Price and Part compatibility.

I’ll address the issue of price first because it is very easily explained. Do not buy or build an AR-10 that you can’t afford to shoot. Not only can the price of an AR-10 be two to three times that of an AR-15, but so can the ammunition.

And while many people own an AR-10 that they shoot like a bolt-action rifle, including myself, they still at least shoot it. I have seen more than one $2,500 wall decoration posing as an AR-10. Sometimes these rifles get sold for a loss without even being properly broken in.

The second drawback is part compatibility. Unlike the AR-15, the AR-10 has developed into more than one pattern of rifle with certain incompatible parts. If you buy a complete AR-10 from the factory this is less important. If you build an AR-10 from parts this is extremely important.

The most popular style of AR-10 is the DPMS pattern rifle. Technically these are LR-308 style rifles, but for all intents and purposes they are AR-10s and I will refer to them as such. Even among DPMS pattern rifles, there is not perfect parts compatibility. The DPMS pattern rifle is the most popular AR-10 style rifle for builders and likely always will be.

Other AR-10 pattern rifles are the ArmaLite AR-10, Knight’s Armament SR-25, and the Rock River Arms LAR-308. These styles of AR-10 rifles are generally sold as complete firearms.

To add to the confusion, AR-10 rifles will share some parts with AR-15 rifles, and certain parts are compatible with more than one pattern of AR-10. Parts meant for the same AR-10 pattern but from different manufacturers can have fitting issues and it is generally good advice to buy the same brand upper and lower receivers.

With all the above-stated issues, there can still be massive money savings in building an AR-10 when compared to buying an expensive factory model. Palmetto State Armory has largely cornered the budget AR-10 market with kits that include everything except the lower receiver.

The lower receiver (for all AR-pattern rifles) is the firearm part that needs to be purchased or transferred through a licensed dealer.

Characteristics of the AR-9

There just aren’t enough of these to go around.

The AR-9 is a fun “little” rifle that developed out of conversion kits meant for the AR-15. I put little in quotations because while they are roughly the same size as an AR-15, virtually everyone describes them as such.

The first AR-9 rifles used a conversion kit which consisted of a barrel, bolt, buffer insert, and magazine block to chamber an AR-15 in 9mm Luger. These guns would then use either Glock 9mm magazines or Colt/Modified Uzi magazines. Less common versions of these kits allowed the AR-15 to be chambered in 40 S&W, 357 Sig, 45 ACP, and 10mm Auto.

Sorry 9x25mm Dillon fans (if such a thing still exists), no factory options are available, yet…

These guns fell under the umbrella term of Pistol Caliber Carbines, or PCC for short. To many of us who grew up watching movies featuring submachine guns like the Heckler and Koch MP5, these kits were a dream come true.

For others, they reduced the cost of shooting an AR-15 by using less expensive ammunition that still had self-defense stopping-power. The last part was always the downside of an AR-15 converted to shoot .22 LR.

A further benefit of chambering an AR-15 in 9mm Luger is the ability to shoot steel targets at close range with minimal bullet splatter and target damage. These guns quickly carved out their own divisions in USPSA and IDPA shooting competitions.

A true AR-9 though uses a lower receiver meant for the 9mm Luger cartridge. Price-wise, they stack up very favorably to an AR-15.

Options still exist for buying an AR-9 that uses Colt/Modified Uzi magazines, but Glock magazine models are the most popular and the clear path forward for the AR-9.

And while most AR-15 and AR-10 rifles are direct-impingement (DI) operated, AR-9 rifles are blowback. Because of this, a heavier buffer (that is incompatible with rifle cartridges) has become the standard.

One of the advantages of converting an AR-15 to be chambered in 9mm Luger can be cost savings if the shooter already has an AR-15 and necessary tools. This also carries the advantage of being able to convert the gun back to a more powerful rifle cartridge at some future date.

Virtually all factory options for the AR-9 use a lower receiver meant for the 9mm Luger.

Buying Decisions

If you read this article in the hopes of educating yourself about a future firearm purchase, remember this is a summary of different types of AR rifles (and pistols too), not a detailed explanation of each one. The goal has been to focus more on application than technical specifications, though there is some of that.

But, my buying advice remains the same; Unless you own an AR-15 chambered in 5.56x45mm or .223 Wylde and have the financial means to practice with it regularly, that should be the logical first choice. Outside of specific needs or compliance with local laws, the golden standard exists for a reason.

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