April 13, 2018: 13 Other Calibers the AR Style Rifle Comes In

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A Brief History

On April 13, 2018, we “celebrate” Friday the 13th, the subject of myths, folk lore, movies and general unlucky business related to the number 13. Or, for some people, 13 is a lucky number! In light of all the bad press the AR platform rifle (M-16 and M-4 family of military carbines adapted for civilian use as “AR” style firearms) has gotten lately, we would like to point out some of the many uses of these modern sporting rifles, at least in part by naming 13 of the calibers these carbines can commonly be found in.

Digging Deeper

Critics of the “Black Rifle” often say, “You can’t hunt deer with an AR-15!” as justification for banning the guns. Well, yes you can. Even in the most common 5.56 X 45 mm caliber you can use soft point or hollow point bullets to hunt deer, though the caliber is not exactly ideal for that purpose. The 5.56 mm or its civilianized counterpart, .223 Remington, is quite appropriate for hunting varmints (crows, woodchucks, prairie dogs, coyotes, etc.) Or other small and medium game. This caliber is also readily adaptable to use as a home defense weapon for those inclined to use a rifle for that purpose. The 5.56 mm chambering is also the favorite among the competitive shooting crowd competing in the extremely popular 3 Gun competition. The accuracy, light recoil, and low cost of 5.56 mm ammunition makes the AR platform carbine highly accessible and easy to train with for people of modest means. Lower priced yet high quality models start at just under $500 and highly modified purpose built long range target or hunting models can cost a few thousand dollars. Here are some common AR calibers and their purpose. (Note: There are a couple dozen more available calibers for AR style rifles and carbines than the 13 we discuss today, even AR lookalike weapons chambered in shotgun calibers, though function systems are different. These AR shotguns are perfectly capable of being used for hunting as well as defensive purposes and are usually found in .410 Bore or 12 Gauge.)

1. .308 Winchester/7.62 X 51 mm NATO.

The original AR rifle was to be chambered in this NATO standard caliber as the AR-10, but the US Military decided to go with the smaller, faster caliber 5.56 mm NATO in order to allow soldiers to carry more ammunition at a lighter weight. Chambered in this standard .30 caliber chambering the AR-10 type rifle is highly adept at taking medium sized game such as Deer, Black Bear, Coyote and the like, as well as providing better long range performance for Law Enforcement use, long range hunting, or target shooting. The 7.62 NATO caliber was widely used by our allies in such weapons as the GR3, the FN-FAL, and the American M-14. Most NATO countries also use this loading in their medium machine guns. Proponents of this caliber often state the wish that the US Military had chosen it over the diminutive 5.56 caliber in the first place.

2. .204 Ruger.

Invented by Ruger in 2004 as an ultra-high velocity varmint cartridge, the .20 Ruger was at that time the only commercial loading in 5 mm caliber and was the second swiftest caliber, capable of launching a 32 grain bullet at over 4200 feet per second. These rounds are devastating on varmints.  Honorable mention to the .22 Nosler,  a ballistic improvement over the 5.56 NATO round giving the .22 caliber AR varieties substantially faster velocity.

3. 7.62 x 39 mm.

Not surprisingly, the second most common carbine caliber rifle platform in the world would also come in the most common carbine caliber in world, the Soviet designed 7.62 x 39 mm round used in the AK-47 family of weapons. For those people convinced that the AK rounds are better for their purposes than the 5.56 mm variety, these carbines and rifles provide the larger diameter and heavier bullets launched at a lower velocity, making the AR platform a viable deer hunting combination of rifle and cartridge. AR style carbines in 7.62 x 39 mm are pleasant to shoot and cheap ammo is readily available.

4. .300 Whisper/.300 Blackout.

Both of these loadings were developed to provide greater versatility to the AR platform, and both are considered interchangeable. The idea is to provide a caliber in 2 different power levels, a sub-sonic loaded cartridge that is compatible with being sound suppressed by a silencer/suppressor, and a supersonic loading that is more capable of taking larger game. A typical loading for the sub-sonic version is a 220 grain bullet at a muzzle velocity of 1040 feet per second, just barely under the supersonic threshold. The higher velocity loading are intended to more or less match the performance of the venerable 30-30 deer loading or the 7.62 x 39 mm AK loading, such as 125 grain bullet at 2200 feet per second. The ability to handle 2 different power levels makes the rifles chambered in these calibers that much more useful, and sorry gun control people, these rifles are mainly intended for sporting purposes.

5. 6.8 mm SPC.

Designed in the early 21st Century by the US Army and Remington, the 6.8 mm Special Purpose Cartridge as a potential replacement for the 5.56 mm loading that was found somewhat wanting in the long distance shootouts in Afghanistan and Iraq. Plus, the 5.56 mm round designed to provide better long range performance (the 62 grain SS109) was found to be less deadly than the original 55 grain loading. The 6.8 SPC bridges the gap between the 5.56 mm NATO and the larger 7.62 mm NATO, both in velocity, projectile diameter, and power (kinetic energy). It would seem to be an effective compromise between the 2 competing calibers, providing close to the low recoil of the 5.56 with little lost magazine capacity and almost the long range performance of the 7.62. Alas, the Military decided to forgo adoption of the new cartridge due to start up costs and complicating the logistics train (not to mention millions of 5.56 mm rounds on hand). This situation is a boon for the civilian and law enforcement customers that decide to choose the 6.8 SPC, one more alternative in the endless variety of AR calibers. (Note: the 6.8 SPC is an interesting enough caliber that several rifle makers offer bolt action and single shot rifles chambered in 6.8 SPC.)  A somewhat similar caliber is the 6.5 mm Grendel, also often chambered in AR platforms.

6. 9 x 19 mm Luger (or Parabellum).

AR-15 and their clones often are found in pistol caliber carbine versions, including full automatic law enforcement only models. In pistol calibers the AR can function in the place of a sub-machine gun for military or law enforcement use, or in semi-automatic garb for home defense and medium game hunting for civilians. The most common pistol caliber found in AR platform carbines is the 9 mm caliber used by the US and NATO militaries (and most of the World) as well as most law enforcement agencies. Fired out of a carbine (16 to 18 inch barrel), these pistol calibers commonly produce 200 or 300 more feet per second velocity to the projectile, making the guns more potent than the caliber would imply. Other common pistol calibers used on AR platform carbines are .45 ACP, 10 mm, .40 S&W, and .50 Action Express.

7. .22 Long Rifle rimfire.

The cheap and ubiquitous .22 LR is an ultra-useful caliber to have as it is found in revolvers, semi-automatic pistols, lever action, bolt action, single shot and semi-automatic rifles and carbines and even derringer type pistols. In the AR platform, this chambering provides the owner with nifty look of the AR type rifle at a lower cost, especially lower cost in ammunition. Exceedingly low recoil and cheap ammo make for a fun, yet economical day at the range or plinking. The .22 LR is also effective on smaller game and varmints. (The rimfire versions of the AR platform differ from the centerfire models in that the centerfire models use direct gas impingement or gas pistons to operate the bolt, while the rimfire models and pistol caliber carbines usually are blowback operated.) Other rimfire calibers found in AR carbines include .17 HMR, .22 Magnum, .17 Mach 2 and .17 Winchester Super Magnum.

8. .458 SOCOM.

Another cartridge developed in response to unsatisfying person stopping performance of the 5.56 mm rounds (especially the M855, formerly the SS10) that was found to be so well stabilized the heavier round was better at long distance accuracy and velocity retention than the original M-16 fodder, but had a tendency to zip straight through enemy combatants without doing much damage or stopping the threat. American Special Operations Command officers brainstormed the .458 SOCOM as a short range highly effective fight stopping round that was no longer than the M855 and would thus work with any AR type lower receiver, only needing a different barrel and chamber. Capable of launching a 250 grain bullet at 2100 feet per second gave this considerable round as much power as a 30-06, nearly triple that of the 5.56/.223. The .458 could also use even heavier bullets, up to 600 grains at 1000 feet per second for use with a suppressor, still supplying 1.5 times the power of the 5.56. The beauty of the .458 SOCOM is that it not only can use the lower receiver of the M-4 or M-16 or AR-15, it can also use the same buffer assembly, and magazine, although each magazine can hold fewer of the big, fat cartridges. (10 rounds in a regular issue GI 30 round M-16/M-4 magazine.) Obviously, the .458 loaded with the appropriate bullet is adequate for just about any big game hunting at shorter ranges in the world. The bullet profile is normally round nosed or flat point.

9. .450 Bushmaster.

With slightly less potent ballistics compared to the .458 SOCOM, the .450 Bushmaster was designed from the start as a civilian hunting cartridge for effectively taking big game out to 200 yards. An advantage over the .458 SOCOM is that you can fit 13 rounds of .450 Bushmaster in a 30 round GI magazine versus only 10 rounds of .458 SOCOM. Sighting in your rifle for point of aim point of impact at 150 yards will result in shooting only 1.8 inches high at 100 yards and 3.4 inches low at 200 yards, making range estimation less critical. The use of spitzer (pointed) profile bullets helps the longer range ballistics. (Other large caliber rounds adapted for the AR platform include the .50 Action Express, .50 Beowulf, and some mid-caliber choices such as .358 Winchester and .338 Federal.)

10. .243 Winchester.

.243 Winchester is a great medium sized game cartridge and varmint taker, fast, fast, fast! Much better suited for deer, feral hogs, and antelope than the 5.56/.223 type of rounds, the .243 (6 millimeter) cartridge sends 90 grain bullets on their way at 3203 feet per second, about what the 5.56 mm round does with a 55 grain bullet. Lowering bullet weight means increased velocity, and with a 55 grain varmint bullet that means over 4000 feet per second of muzzle velocity. Smokin’! Even using bullets up to 115 grains can achieve velocities of 3000 fps or more (in barrels of suitable length, such as 24 inches). The .243 Winchester is based on the .308 Winchester (7.62 x 51 mm NATO) case necked down to caliber. This caliber choice can make your longer barreled AR platform rifle much better at longer ranges and for taking medium game.

Question for students (and subscribers): What other AR platform calibers are you fond of?  Please let us know in the comments section below this article.

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Historical Evidence

For more information, please see…

Howlett, Doug. Shooter’s Bible Guide to AR-15s: A Comprehensive Guide to Modern Sporting Rifles and Their Variants. Skyhorse Publishing, 2016.

Reaser, Rob. AR-15 Rifle Builder’s Manual: An Illustrated, Step-by-Step Guide to Assembling the AR-15 Rifle. CreateSpace, 2016.

The featured image in this article, a photograph by TheAlphaWolf of an AR-15 rifle with a Stag lower receiver California legal (only with fixed 10-round magazine), has been released into the public domain worldwide by its author, TheAlphaWolf.


About Author

Major Dan is a retired veteran of the United States Marine Corps. He served during the Cold War and has traveled to many countries around the world. Prior to his military service, he graduated from Cleveland State University, having majored in sociology. Following his military service, he worked as a police officer eventually earning the rank of captain prior to his retirement.