The Difference Between an AR-15 and AR-10

Posted in: Rifles Tactical


It is this author's opinion that the greatest takeaway from the history of the AR platform is that it was born and bred in Hollywood, CA. Oh, sweet, sweet irony.

Imagine being born in a town that makes BILLIONS of dollars by exploiting you but also thinks you should be illegal. Weird.

But that's not why you're here. You're here to learn the difference between an AR-15 and an AR-10 rifle, and I'm here to help.

This article will cover the unique features that set the AR-10 and AR-15 apart as well as the similarities that keep them forever intertwined.

It's easy to confuse the AR-15 and the AR-10 because to the average person (that's me), they look exactly the same. They use the same style receivers constructed from the same material complemented by the same mechanisms that are manipulated in the same way. That's a lot of 'the same'.

And although the differences are subtle, they are also significant.

Let's start with a broad overview.

An Overview of the AR-15 and AR-10

The easiest way to tell the difference is to take a look at the magazine well (commonly called the magwell). This is the easiest and most obvious way to tell if you're looking at an AR-15 or an AR-10. The AR-10 magwell is just a bit bigger than the AR-15.


  • The AR-15 magazine well internal dimensions are approximately 2.4' x 0.9' with the AR-15 magazine being sized to function with cartridges with up to 2.26' overall length*.
  • The AR-10 magazine well internal dimensions are approximately 2.96' x 1.16' with the AR-10 magazine being sized to function with cartridges with up to 2.83' overall length*.

(*Overall length measurements here are industry standard and may vary slightly based on specific magazines).

Outside of the magwell size, the two platforms look nearly identical, but there are some significant differences.

Things that are different:

  • Caliber
  • Size of the receivers
  • Magwell
  • Bolt catch
  • Mag release
  • Pivot pin
  • Handguard size
  • Barrel nut
  • Bolt carrier group (see above)
  • Charging handle
  • Buffer tube
  • Buffer


Things that are the same:

  • Trigger
  • Safety
  • Buttstock
  • Pistol grip
  • Castle nut

To be clear, all of the items look the same and are really only different in their dimensions. The components perform the same features in each gun, but they have to be built to different parameters.

Both rifles are built on the same basic design that was born in the labs of ArmaLite in the 1950s in Hollywood, CA. At that time, ArmaLite was a small engineering outfit with less than ten employees, but by 1954 the US Air Force had already adopted one ArmaLite design: the AR-5. The AR-5 was/is a bolt-action .22 Hornet rifle designed as a life-saving/survival rifle for pilots to tuck into the tight space of a cockpit. Its greatest advantage was the ability to break down and then store all working components inside of the buttstock. In the broken-down configuration, the rifle was airtight and able to float. A perfect setup for combat pilots.


In 1955 & 56, the US Army was looking to replace the M1 Garand at the go-to battle rifle for the American soldier. ArmaLite's Chief Engineer was Eugene Stoner who was now faced with the task of offering the military an alternative to the M1 Garand - a 10 pound behemoth that held just eight rounds of 30-06 ammunition, but had been dubbed by General George S. Patton as the 'greatest battle implement ever devised.'

Armalite was breaking new ground by using lightweight materials such as fiberglass and aluminum in its designs, and with the success of his AR-5 survival rifle design, Chief Engineer Eugene Stoner had experience in matching the military's needs with a unique design. In working to win the contract to replace the M1, Stoner would eventually offer a rifle designed to hold twenty rounds of 7.62x51 and weigh less than eight pounds. That would become known as the AR10 rifle.


The AR-10 had a Waffle Patterned Magazine and a charging device that looked like an upside-down trigger that ran through a channel cut through the top of the upper receiver. A 'carry handle' helped cover the charging handle while giving a place for the rear sight to be seated.

ArmaLite presented the AR-10 as the 'world's most advanced combat rifle' due to its lightweight, its highly effective caliber, and its ability to fire rifle grenades with no adjustment being necessary to the rifle itself. The user would drop a rifle grenade stem first into the muzzle of the rifle and then use grenade-propelling rounds in the issued magazine to launch the grenade. Pretty impressive.

The barrel was a steel composite wrapped in aluminum and the cylindrical design of the bolt carrier group was said to allow the higher pressure of the 7.62 x 51 round to be manageable due to the dispersion of the gas evenly along the length of the rifle's lightweight body. Corrosion-resistant material, ease of assembly, and interchangeable parts reduced the service and maintenance of the AR-10 to an 'absolute minimum.' ArmaLite also boasted that the AR-10 was able to function longer than any other rifle without cleaning or lubrication.

From the barrel to the stock, the rifle was composed mainly of alloys and plastic which required a design that would, unfortunately, fail during military testing.

The US military refused the AR-10 when an early submission had a round explode the barrel. Refusing the AR-10 from ArmaLite meant The Springfield T44 would win the contract and become known as the M-14, adopted for use in 1957. Stoner himself would later suggest that the loss to Springfield was more about politics than anything else.

However, ArmaLite did win contracts for the AR-10 with Cuba, the Republic of the Sudan, and Portugal soon thereafter. But ArmaLite wasn't really keen on mass production. That's why the earliest AR-10 rifles were mostly produced in the Netherlands. Forgotten Weapons has a fantastic piece on the evolution of AR-10 production if you really want to geek out on it.



Throughout the Korean War American soldiers began to find that weight, rate of fire, and range of effectiveness were top priorities that needed to be addressed in the military's next battle rifle. In Korea, 600,000 Chinese fighters lost their lives. The Chinese soldiers were notorious for their hard charges up hills and across the battlefield, and it was not uncommon for thousands of Chinese soldiers to attack an American position simultaneously.

The American soldier in Korea was outfitted with a heavy M1 Garand rifle that weighed almost ten pounds, held a mere 8 rounds, and had a firing rate of about 50 rounds per minute. Imagine thousands of enemy fighters charging your location and you have only eight rounds at the ready. Sounds like a bad idea.

The AR-15 was designed to address these concerns. The rifle was lighter overall (weighing around five pounds) and used a smaller caliber round (.22) which not only reduced weight, it also added to the combat effectiveness of the weapon. Eugene Stoner said,

"There is the advantage that a small or light bullet has over a heavy one when it comes to wound ballistics. ' What it amounts to is the fact that bullets are stabilized to fly through the air, and not through water, or a body, which is approximately the same density as the water. And they are stable as long as they are in the air. When they hit something, they immediately go unstable. ' If you are talking about .30-caliber [like a bullet used in the M-14], this might remain stable through a human body. ' While a little bullet, being it has a low mass, it senses an instability situation faster and reacts much faster. ' this is what makes a little bullet pay off so much in wound ballistics."

The reduction in weight would allow the American soldier's combat load to not only get lighter but also provide that soldier better defense capabilities due to the increased amount of ammunition he could carry. Despite those advantages, the US Military initially refused to sign on to the idea of the AR-15.

Who you ask determines the answer you will receive as to why.

What is known for sure is that the AR-15 initially performed poorly during testing which prompted Eugene Stone to personally fly out and evaluate the issues. Stoner determined that military armorers had altered parts of the rifle in ways that rendered it inoperable or ineffective. However, he was unable to convince the higher-ups at the time that his findings were the cause of the issues.


In 1959, just a few short years after losing its bid to replace the M1 Garand, ArmaLite inked a deal with Colt Firearms to sell Colt the design for both the AR-10 and the AR-15. Colt was then able to sell early editions of the AR-15 to what was then called the Federation of Malaya (now known as Malaysia).

At the same time, the conflict in Vietnam was escalating. There were several hundred American advisers in Vietnam, but no combat roles were being taken on by US troops. Once Army Rangers actually began assisting in Vietnam, the AR-15 was acquired for testing in their battle arena and was met with rave reviews from the Rangers.

President Kennedy's Secretary of Defense, Robert McNamara, turned the tide for the AR-15. McNamara wanted one rifle to cover all branches of the military. He viewed mass production as a way to control quality while keeping prices down. The military ultimately adopted the AR-15 which would be the M16-A1 rifle put into service in Vietnam in 1965.


The M16 went into full production in Colt's facility with 45,000 guns rolling off the assembly line every month at its peak. However, the initial implementation of the M16-A1 was a failure by most accounts.

There were early problems of malfunctions reported in the field, and one soldier even penned a letter to his Senator saying he had seen American soldiers die because their rifles were failing during battle. That soldier's Senator was Gaylord Nelson of Wisconsin who made the letter public. The letter prompted Congressman Richard Ichord of Missouri to begin an investigation of the rifle and its failures. One of the most notable findings was that in the initial testing of the rifle, the ammunition used was loaded with stick powder, but the military switched to ball powder for the issued ammunition. Ball powder is not only exponentially dirtier, it is also negatively affected by exposure to moisture. If the ammunition was exposed to moisture, it would swell and cause rounds to become lodged in the chamber. Soldiers in Vietnam learned quickly that they could not leave a round in the chamber for extended periods of time. Soldiers would have to unload their rifles before sleeping to keep the rifle from becoming jammed up by a swollen round (a result of the constant moisture in the air of the tropical jungles of Vietnam.)

Adding to the list of bad ideas from the government, the military told the soldiers that the rifles were self-cleaning and then issued the rifles without cleaning kits. Dirty barrels, bolt carrier groups, and poor ammunition all created a deadly recipe for the American soldier on the battlefield. One other important element is that the Department of Defense actually regressed the American soldier's weapon in a sense by denying requests from the military to chrome plate the chamber of the M16. Once cleaning kits, proper ammunition, and retrofitted chrome-plated chambers were in place, the failure rate of the M16 fell drastically.

Today, in its many forms and variations, the AR-15 rightfully stands as America's favorite rifle platform, providing both sport and security to the American civilian and the American soldier. Eugene Stoner's design and the respective efforts of ArmaLite and Colt to bring it to fruition continue to play a pivotal role in providing liberty and safety to oppressed and endangered people around the world.


Both the AR-15 and AR-10 are capable of housing multiple calibers.

Here is a non-exhaustive list of the separate but equally impressive capabilities of the two.

AR-15 Calibers: 

AR-10 Calibers:

Thank you for shearing, great info and history
John Wheatman
Fantastic read. Thanks Kris.
Todd Pruett
Very informative article. Learned a few new things especially about the problems in the beginning stages.
Jon R Tatum
Great article, interesting history, lots of good information. Thank You
You completely overlooked a major item of History of the AR-15 and the USAF. The USAF was the First to be issued the AR-15 and The Father of Strategic Air Command aka SAC, General Curtis LeMay. The other branches got them after the USAF/SAC got them. All of the M-16s I handled and saw in the USAF were stamped COLT AR-15 and were Select Fire. McNamara did not allow the chambers to be Hard Chromed which allowed the bolt to rust and freeze up. The USA/Army issued a comic book that told the troops how to properly maintain the weapon. I used to have several of them still sealed in the plastic wrapper they came in. Lost them over the years. Here is a link that adds to your History article.
As a military recruiter who worked at the Armed Forces Examination and Entrance Station (AFEES), these manuals were in comic book form because a majority of the Army's 'cannon fodder' had only a \"3 1/2 grade\" reading level\". The main character was a large breasted, attractive woman in tight fitting coveralls. The Army was hoping the comic format would gain and hold the soldier's attention long enough for him to learn how to properly maintain and use his weapon. There were comic books for other Army jobs but I do not recall which.
Don Bailey
Well written article, thank you for breaking this all down for us, the audience.
As a military recruiter who worked at the Armed Forces Examination and Entrance Station (AFEES), these manuals were in comic book form because a majority of the Army's 'cannon fodder' had only a \"3 1/2 grade\" reading level\". The main character was a large breasted, attractive woman in tight fitting coveralls. The Army was hoping the comic format would gain and hold the soldier's attention long enough for him to learn how to properly maintain and use his weapon. There was comic books for other Army jobs but I do not recall which.
Eugene Teasley
Speaking of AR history, will PSA do a A1 style lower? The only places to pick them up now are pricey and the receiver markings aren't anywhere near correct like you guys are doing. I love the old ARs and really want to build one or six of my own.
We are working on a proper M16A1 at the moment. I do not have a date as far as release.
curtis kreutzberg
I have and love several of your AR10s and AR15s. I'd love to see you design an AR lower to accommodate the 338 Lapua cartridge . Everyone would love it, it would become the industry standard for big bore AR's. I'd be tempted to strech out from my current 600 yards to 1000+ if I could get an affordable PSA 338, lord knows I don't need another rifle but that would tempt me greatly.
It isn't in the plans at the moment, but we do shoot our PSA 6.5 Creedmor out to a mile regularly!
Robert Lawson
I would really like your ideas on a 6.5 Creedmore
Richard Hill
Can’t seem to remove the barrel nut from a PSA 15. What should I do any suggestions. In the Columbia, SC area.
Jerry Simmons
Purchased an AR-10 from a local vender. I was told at the time it would shoot either the .223 or 5.56 rounds. Reading your article, the AR-10 will not accommodate either round. Have I been duped? Thanks.
You bought an AR15 multi-cal Duped
Gregory Romeu
The left side of the mag well should be clearly marked with the caliber of the firearm. If you have an AR-10, then it is most likely a .308 / 7.62x51, HOWEVER, as per this article, if you scroll up and review the photo that has ALL the CALIBERS for BOTH the AR-15 and the AR-10 printed along side of each type of rifle it tells you what caliber fit in each configuration. BUT IT ALL DEPENDS ON THE CALIBER SIZE OH "YOUR" BARREL AND CHAMBER. it you cannot figure it out, take your UNLOADED firearm to a local gun store or gunsmith and ASK QUESTIONS.
1st I want to say I got the AK103 premium yesterday and I’m stoked!.....My question is does PSA ever plan on having CHF FN AR10s?
We don't have any plans for this year, but that is not to say it will never happen.
Ted Matuga
Great article and great comments by all. Informative and enjoyable!!!
Larry Rogers
Thanks for the great site, merchandise, and info!
Austin Asseff
Solid article! Any hope of AR 10 pistols comming soon on PSA?
Maybe in the long-term future. There is nothing in the immediate plans now though.
AR-10 Carbine Buffer for .308 Features and Specifications: 3 Ounce Buffer Weight 2.5" Overall Length Color: Matte Black
barry parker
I love articles that teach you something, thank you. makes me love the AR-15 more.
mike sorak
Do you have any Info on Cold treating the barrels? It changes the molecular structure @ 300 degrees below zero . The auto industry let me experiment with treating tool & die steels. Fantastic results. I did do a couple of barrels. Stabilizes accuracy as the barrel heats up .
The Army issued the "Preventive Monthly Maintenance" books to cover topics from rifles to driving vehicles to proper care of issued clothing. Some were definitely a bad comical form for important items, like the "Star Wars" themed one for goer driving.
I wish I could find affordable 12 gauge upper for an AR-10 that would shoot cheap shotgun shells reliable
Thanks for the article, just made my list of things to buy a bit longer.
Matt Cannon
This is a good, yet basic article --the follow-up article should point out the differences between AR10/SR25/DPMS pattern rifles and the capability of parts...There are a lot of differences and they can really confuse amateur and novice builders alike.
Interesting to learn that Arma-Lite was a very small engineering company founded in Hollywood, California in 1954. The story also tells me that Colt Firearms bought the name and patented technology from Arma-Lite. Hence, the AR-15 became the M-16 when our military bought it from Colt.
Michael Robertson
Interesting article. Add to this that the design that Eugene Stoner brought to the table was the Stoner 62. Also if memory serves me correctly, the Air Force had a couple different versions of the rifle issued. One was a prior deal to the A1 designation and the other was I believe called CAR15. Which was a scaled down version. Thank for a pretty informative piece.