AR-10 vs. AR-15: A Comparison

While working for Fairchild ArmaLite, a California-based aviation company, firearms genius Eugene Stoner in the mid-1950s developed a lightweight automatic rifle — the original assault rifle, if you will.

His ArmaLite Rifle Model 10, often just called the “Armalite Rifle”, remembered today simply as the AR-10, was a radical departure from the wood and steel rifles that preceded it, incorporating high-impact polymers, aircraft-grade aluminum upper and lower receivers, and a piston-less direct gas impingement operating system. 

Chambered in 7.62 NATO, the 6-pound AR-10 Armalite Rifle was submitted for trials with the U.S. Army who went instead (surprise, surprise) with the more traditional M-14, a wood and steel rifle the service had developed in-house. 

The AR-10 died out for a generation when Army Chief of Staff General Maxwell Taylor selected the M14 over the AR. It stayed in mothballs until Eagle Arms rebooted the old concept in 1995 while at the same time Stoner himself, who had moved on to work for Knight’s Armament Company, upgraded the design to his Stoner Rifle Model 25, or SR-25.

Added to this are .308/7.62 NATO spinoffs of the AR-15 platform such as the LR-308. 

All of these today are often just lumped in the “AR-10” category, often erroneously referred to as the first assault rifle.

More on this in a minute.

Tasked by ArmaLite in the late 1950s to develop a scaled-down .223 Remington-chambered rifle from Stoner’s original AR-10 concept, Stoner’s assistant, Robert Fremont, along with Jim Sullivan made a series of changes to the preceding battle rifle’s design to produce what is now forever enshrined as the ArmaLite Model 15, or AR-15, which was submitted for testing by the U.S. Continental Army Command for consideration as a replacement for the very long-in-the-tooth M1 Garand.

This smaller cartridge was lighter than the .308 and could provide more firepower and more round per combatant than the M1 Carbine, Thompson Submachine Gun, or M3 “Grease Gun” while offering a much lighter package than the BAR Browning Automatic Rifle and M1 Garand.

Throughout the early years in Vietnam, the AK-47 was putting the M14 to shame, so Uncle Sam was looking for something to even the battlefield. Even though the AR-10 was eventually passed on for the M14, U.S. Army Special Forces saw the potential of the AR-15, and after passing positive reports from the field back to command, Secretary of Defense Robert McNamara ordered an assessment of these space-age lightweight rifles.

While the AR-10 died out in the Disco-era, while its smaller half-brother, the AR-15 shot to international prominence as Colt picked up the patents in 1959 and aggressively started marketing their semi-automatic rifle, winning military and law enforcement contracts while simultaneously bringing “sporter” variants to the commercial market. 

By the 1980s, Colt lost market share to small AR makers such as Olympic and Bushmaster, a trend that continued until over 100 companies were making AR-15 pattern firearms by 2015. 

Today, AR-15s are being produced by everyone from niche makers who might crank out 100 guns a year to household firearms manufacturer names like Ruger, Savage, Sig Sauer, and Smith & Wesson. This diversity has meant tremendous expansion and variety in the market, but more on that in a moment.

While the AR-10 was unsuccessfully pitched to the military in the 1950s, the follow-on AR-15 managed to grab the golden ring in 1962 with Colt’s first U.S. Air Force contract and continues to hold on to it today with M4 contracts currently being filled by not only Colt but also Daniel Defense and FN. 

The most important side effect of this military success, with millions upon millions of guns delivered to the U.S. and its allies over the past six decades, is that the AR-15 and its subsequent M16A1/A2/A3/A4/M4/M4A1 descendants have gained the all-important benefit of standardization. 

Curious how the AR-15 compares to the M4 Carbine? You can read more about the AR-15 vs M4 here

For example, a Vietnam-era grunt from the 1960s who went through his basic marksmanship instruction with an early Colt M16A1, if sent via time machine to the present day could pick up a fresh-from-the-assembly-line FN-made mid-length gas system M4A1 and be able to not only load and fire it but also clear the most common malfunctions then field strip the carbine to maintain it.

The current Army technical manual (TM 9-1005-319-10) on the platform covers maintenance on all models with extraordinarily little variation in procedures. This is because the rifle has become the baseline.  

The same “mil-spec” standardization is the steady goal post for the hundreds of AR-15 models on the commercial market today.

By and large, AR-15s on the market now can use and accept just about any “standard” 26-item lower parts kit to include the trigger group and pistol grip, all of which can be upgraded with more custom drop-in parts. 

Even $5,000 high-end ARs with all the bells and whistles can usually use $50 vanilla GI-style LPKs in a pinch. The same can be said for upper receivers, with the standard nine-item bolt carrier group interfacing on typical DGI-system guns in compatible calibers.

Likewise, handguards and rails, limited only by the length of the barrel, can be readily swapped out. 

The same can be said for magazines, with NATO in 1980 drafting a STANAG-compliant standard– that being the AR-15 mag pattern—which brought consistent magazine capacity to the masses when the STANAG standard was copied by the Israelis, Spanish, French, Italians, and even the South Koreans and Poles.

The only moment of pause when it comes to AR-15 modularity surfaces on buttstock options because there is a dimensional difference between the mil-spec and commercial types of buffer tubes, and in differences in the uppers when direct impingement is dropped for a short-stroke piston action. 

The same cannot be said about the AR-10. As the platform died out for a generation and was only resurrected in the 1990s by widely different interests, there was a more varied approach to its modern development. 

As such, there isn’t a “mil-spec” standard to the modern AR-10, although to be sure a couple of models– HK’s 417 and KAC’s SR-25– have been adopted by the military.

For instance, not all use SR-25/M110 pattern magazines with some guns using a proprietary mag, FN FAL type mags, or some other design. DPMS/Panther LR-308 type uppers and lowers– which use a round-end cut– will not interchange with other SR-25/M110 receivers which use a slant-ended cut, although both types are often incorrectly lumped into the same “AR-10” category.

ArmaLite and DPMS even used different barrel thread pitches– 18TPI-3A for one, 16TPI-2A for the other– requiring different barrel nuts. 

The same mismatch goes for more minor parts like mag latches, bolt carrier groups, buffer and gas tubes. 

When it comes down to it, about the only universally interchangeable AR-10 parts these days are some lower components like the trigger guard, safety selector switch, takedown pins, castle nut, and trigger. Meanwhile, on the upper, you are looking at minor parts interchangeability on items like the dust cover and charging handle.

There is some good news on this front. While originally there was virtually no interchangeability between the two ifles, in recent years, there has been a greater drive to borrow from the AR-15’s widespread standardization to make the AR-10 more modular. 

The best cases of this are in SR-25-style platforms which tend to accept many of the AR-15’s internal parts, including pins, buffer tube, gas tube, springs, and triggers.

This has extended to the use of industry-standard AR-15 dimensions to allow for greater compatibility with 5.56 handguards and LPKs along with comparable production and testing. 

There has forever been a near-default 25-round magazine design, that of the 308 PMAG LR/SR, which of course is based on Magpul’s wildly popular 30-round 5.56 PMAG for the AR-15. You can bet that this trend will continue until about the only difference between AR-10 and AR-15 within another generation will be in the dimensional size of the lower to accept the larger cartridge/magazine and in the likewise up-sized BCG, chamber and barrel. 

Moreover, across the evolutionary arc of the two rifles, elements of the AR-10 such as the nomenclature and manual of arms have increasingly morphed to mirror those of the AR-15. These days, the surface controls, layout, and “feel” of the two AR rifles are much the same, with the AR-10 simply being a larger format. 

Whereas the previously mentioned 1960s Army recruit trained on the M16A1 would have been a bit confused to be handed Mr. Stoner’s original AR-10 back in the day, today he could pick up what is seen as the AR-10 of the present and be able to figure it out in short order.

While the AR-10 started in 7.62 NATO.308 Winchester and the AR-15 followed in its wake chambered in 5.56 NATO/.223 Remington, and it remained that way exclusively for over 20 years. Today there are more than 50 factory caliber options in the two platforms, not counting wildcat chamberings and custom research builds looking to achieve stratospheric muzzle velocity or unusable rates of fire. 

An AR-10’s muzzle velocity will generally range between 2600 to 2800 fps, while the smaller-caliber AR-15 will put up 2700 to 3200 fps, depending on bullet grain and powder load, of course.

Using the standard AR-15-sized lowers and magazines with dedicated lowers in companion calibers, AR-15 users can take advantage of the highly suppressible .300 AAC Blackout for sporting and CQB and home defense uses.

For those wanting to stretch things out past 300 yards, there is the .224 Valkyrie for long-range hunting or target shooting, while varmint hunters may opt for something more like .204 Ruger.

For more oomph, there is 6.8 SPC, developed for military uses out to 500 yards with better performance than the standard 5.56 or 6.5 Grendel which brings much the same bonus. 

Scaling up from there is the .458 SOCOM. Hunters, especially in states which have carve-outs for sportsmen using rifles chambered for “straight-walled” cartridges, are enjoying the .350 Legend and .450 Bushmaster which has proven itself not only against hog and deer but elk and bear as well. 

Then there is the moose-capable .50 Beowulf, which carries up to a 400-grain pill for big game hunting. Plinkers can opt for a dedicated .22LR AR-15 or utilize a rimfire upper such as those made by CMMG to go sub-caliber.

As such, the AR-15 is almost a universal adapter when it comes to rifle calibers, at least for short, typically under 500 yards, ranges. 

Where the AR-10 excels at, compared to the AR-15, is in the fact that the parent .308 Winchester case size used in its magwell is an excellent starting point for longer-cased rounds.

This was seen in some of the first .243 Winchester-chambered rifles which ArmaLite began marketing in 1995 in their AR-10 rifles. Likewise, such traditional bolt-action hunting rifle cartridges as .260 Rem, 7mm-08 Rem, and 6.5 Creedmoor have appeared in these outsized ARs.

Additionally, the .308 Winchester has lent its case to optimized ARL loads like the .338 Federal and .358 Winchester, both of which are seen in AR-10s. Stretching things even further, there are chamberings for .300 RSAUM, a cartridge based on the safari-grade .404 Jeffery, and the straight-wall .500 Auto Max, which has been described as being “absurdly powerful” for those interested in taking stopping power to the danger zone.

For those wanting to push out to distances past 500 yards, or bring a lot more with them ballistically speaking, the AR-10 gets the nod.

Fundamentally, the choice between AR-15 and AR-10 comes down to the user’s intended purpose.

For sure, the AR-15 is much more common and includes accessibility to perhaps the world’s largest array of aftermarket accessories and parts.

Meanwhile, the AR-10 is more select but is growing in popularity– after all, it took about 20 years off in the 1970s and 80s while its little brother was running laps and getting better. 

The line between the two is getting increasingly blurred. Today, it is possible to have a 7-pound AR-10 build and a 12-pound AR-15 build, so weight is increasingly less of a tipping point, especially if the user opts for skeletonized parts and fluted or carbon fiber barrel. Besides, AR-10s are utilizing more AR-15-standard parts than ever before, for instance in triggers. 

In the end, it comes down to caliber choice or, to be more specific, a choice between the two groups of calibers as uppers are readily changeable and in a variety of barrel lengths designed to maximize intended performance – be it gross firing power, long-range, or home defense.

Should you want a platform optimized for calibers such as 5.56 NATO, .300 BLK, and .350 Legend, then the AR-15 family is where you want to be. 

On the other hand, if you want to walk in a world of .308 Win, 6.5CM, and .358 Win, then you may find yourself to be an AR-10 guy. 

Either way, the choice is yours.

• National Museum of the United States Air Force, Security Police Weapons, May 20, 2015
• Firearms History, Technology & Development, What is a STANAG magazine?, August 3, 2012
• Todd Burgeen, Big Horn Armory AR500: Testing the Absurdly Powerful AR in .500 Auto Max, April 17, 2020
• Christensen Arms, AR-10 Carbon Fiber Barrel