AR-15s are popular for many reasons. Specifically, target and range shooting, long-range shooting, home defense, and lately a surge in popularity as a hunting rifle. They are lightweight, accept accessories easily, are adaptable, and most importantly, they are modular. It isn't easy to keep up with the chamberings that AR-15s come in nowadays. New calibers in AR-15's and the available ammunition seems to expand every year or two. There are the most popular calibers such as .223 Rem and 5.56 Nato, and as of late, the growth in popularity of the 6.5 Creedmoor may indicate another favorite chambering. There are so many AR-15 caliber offerings. Let's just say that they range from .22 to .50 Beowulf. Okay, if you want a more definitive list, here ya go: .223 Remington, 5.56x45 NATO, .224 Valkyrie, .25-45 Sharps, 6.5 Grendel, 6.8 SPC, .300 Blackout, 7.62x39, .338 Spectre, .450 Bushmaster, .458 SOCOM, .50 Beowulf, and about fifteen to twenty more that have CIP or SAAMI specifications. The ones that I listed above are the calibers that are the easiest to find ammunition for.

MAGAZINES

The capabilities and also the limitations of an AR-15 to accept so many calibers has a little bit to do with magazines. It's true that the magazine is designed to fit the cartridge, however, the lower receiver of an AR-15 must accept the magazine. So let's define an AR-15 magazine as any magazine that is compatible with the standard AR-15 lower receiver. Not all of the aforementioned calibers use the same magazine, but they still use a magazine that is compatible, of course, the rest of the firearm must also be configured to accept and shoot that cartridge. The possibilities of an AR-15 build are endless. Build Kit and individual parts for a build are very popular right now. You or someone making an AR-15 custom build for you can dream up anything to make the AR-15 exactly what you want.  

POPULAR AR-15 CALIBERS WITH COMMONLY AVAILABLE AMMO

Popular calibers and easy to find ammo are what most buyers desire. I will refer back to my earlier article on AR-15 ammunition and I will add some caliber-specific pros and cons to help you decide what AR-15 caliber is right for you. With so many to choose from, you will have an easy time choosing the caliber that is right for you and what you intend the firearm to be used for.  

.223 REMINGTON

PROS:
  • Great selection of powder loadings available, from 36gr. to 90gr.VLD
  • Lethal to 300 yards, up to 500 yards with 90gr. VLD
  • Popularity of this standard caliber means that there is a great supply of magazines, ammunition, parts, and accessories readily available.
  • Reloading is easy and it produces pretty accurate rounds
  • Excellent Accuracy
  • Low Recoil
  • Lightweight and easy to carry
CONS:
  • Sensitive to the rifling twist
  • Not a recommended round for big game hunting
  • Lower energy could mean less penetration
  • Bullet can be affected by wind
  • Low mass and smaller diameter results in less knockdown power at longer ranges


Classic Firearms AR-15 223/5.56/.300BLK 30 Round Enhanced Magazine w/ Yellow/Gold Accents

5.56 NATO

PROS
  • Fast and light ammo
  • Low recoil
  • Most rifles chambered in 5.56 are more compact
  • 100 rounds of 5.56 with 55gr. ammo weighs only 2.6lbs.
  • Highly accurate due to low recoil, easy to keep on target
  • Lethal up to 600 yards
  • Very light round gives assault rifle rifles controllable firepower
  • Easy to fire in full auto due to very light recoil
  • Efficient on the battlefield
CONS
  • Not great in an SBR
  • 1st round penetration usually wounds, takes two to three rounds to stop the threat


AR-15 Steel .223/5.56 40rd Magazine

300 BLACKOUT

PROS
  • Great round for SBR's
  • Does not lose a lot of velocity when used in shorter barrels
  • Subsonic loads are a lot more friendly to the ears
  • Great round to use with suppressors
  • If used for home defense, not likely to over-penetrate
  • Hard-hitting round with reliable knockdown power
  • Reloaders love this caliber
  • Low Recoil
  • Great for varmints and mid-sized game
  • Terminal velocity
CONS
  • Not great for long-range. Developed for sub 200yrd. range
  • Expensive
  • Sometimes hard to find


Hexmag AR-15 5.56/.223/.300 Black 30 Round Magazine

6.5 Grendel

PROS
  • Excellent accuracy
  • Very little velocity drop to terminal range
  • Good energy at the target
  • Low recoil
  • Big bang in a petite package
  • Less wind interference in flight
  • Growing in popularity
  • Becoming easier to find
  • Reviews on the ammo for this caliber have been consistently positive
CONS
  • Hard to find reliable magazines for this ammo
  • Dies and parts are expensive
  • Peak performance is usually achieved in a longer barrel (20"). Longer barrels defeat the purpose of more compact AR platforms.
  • Needs not only a barrel but also a bolt to adapt a 5.56mm rifle to it.


Alexander Arms 6.5 Grendel 24rd Magazine

204 RUGER

PROS
  • Very accurate
  • Easy on the ears
  • Very low recoil
  • Shoots flat to 300 yards
  • Still terminal at 400 yards
  • On target faster and straighter
  • Retains energy
  • 4000 fps
  • Many five star reviews
  • Some ranges will not allow
CONS
  • Not intended for larger game
  • Ammo, brass, bullets a little more expensive than most AR ammo
  • Small rounds could be affected by wind (its speed usually negates the wind affects, however)
  • Very specialized AR platform


Hornady Superformance 204 Ruger 40gr V-Max Ammunition

6.8 SPC

Pros
  • Very Accurate
  • Two times the ballistics of a 5.56mm
  • Great stopping power
  • Performs well in SBR's
  • Accurate reloads
  • Switch magazine and an upper to make a 5.56mm into a 6.8SPC
  CONS
  • Expensive, about a dollar per round, give or take a few pennies
  • Hard to find
  • Needs a caliber specific bolt and magazine
  • A little more recoil which means slower follow-up shots
  • Not a great selection of reloading supplies


Ruger SR-556 6.8 Remington SPC 25rd Magazine

458 SOCOM

PROS
  • Big bore cartridge for an AR
  • Extremely accurate out to 200 yards
  • Can achieve 1600 to 3000 ft./sec. (will be lower with heavier bullets)
  • Big game hunting
  • Immediate stopping power
  • 100gr. to Subsonic 600gr.
  • More bullet selection
  • Great with suppressors
  • Larger than 450 Bushmaster and 50 Beowulf
  • Headspaces on the shoulder
  • Can use standard GI magazines or lancers
  • Specialized upper can be mounted on any AR-15 lower to accept ammo
CONS
  • Probably need to reload unless you can afford a couple of dollars per round
  • Brass is hard to come by
  • Sometimes you have to wait for your favorite store to carry this ammo


C-Products 458 SOCOM 10rd Magazine

Some AR-15s can also shoot pistol ammunition such as 9mm, 40S&W, and 45 Auto.

FINAL THOUGHTS

When deciding on what AR-15 caliber is right for you, ask yourself what do you want the firearm to do? Usually AR-15 owners select their caliber to serve multiple purposes. With so many parts available, building your own AR-15 is more popular than ever. Check out Classic Firearms' build kits. 80% lower receivers are also a great option for your AR-15 build. The caliber availability in these lowers is growing and you should be able to find the 80% lower caliber that you desire. Shop All Mags & Drums
Shop All Ammunition
Shop All AR-15 Style Rifles