The AR pattern rifle is the most popular shooting platform in the USA. Anyone who owns one will tell you it offers unrivaled versatility and modularity when it comes to how you configure it to both look and perform.
But I’ll confess, I didn’t always realize that. For a time, I believed this style of rifle only came in one flavor: the 5.56×45-based M-16-variant I trained with way back in the early 90s. While 5.56×45 (and .223) may be what the majority of AR-15s are set up to shoot, there are literally dozens of other caliber choices out there that are potentially better suited for different applications.
Thinking there may well be others naively clinging to similar misconceptions, I wrote this article to help educate anyone interested in choosing a different AR caliber. The goal here is to keep things in layman’s terms, skipping the hardcore numbers and charts, and certainly not to weigh-in on the “which is better” argument. As we always seem to be saying, there is no “best” choice. Each does one does something a little better than others, while at the same time doing something a bit worse than the others. Your own needs and circumstances will determine which will be the best fit for you, and hopefully after reading this, you’ll have a better idea of which direction you want to take your first or next AR-15, caliber-wise.
Why do alternate calibers exist for the AR-15?
While the 62gr 5.56×45 round has seen widespread military and paramilitary use, it’s considered a borderline caliber when it comes to hunting anything more than varmints. Most of the AR’s alternate calibers were created in attempt to address this by shooting a larger, heavier bullet. Not only is this a more humane when hunting, but a heavier bullet is less susceptible to deflection when shooting in brush or treed environments. Others trend more towards being effective in self or home defense scenarios – especially in urban environments – where the high velocities of rifle rounds aren’t ideal for indoor, close-quarters use.
What should I know when it comes to choosing an alternate caliber?
The main thing to keep in mind when it comes to AR-15 calibers is that there is no “magic bullet” (pun intended). Everything is a trade-off. An AR-15’s magwell opening is a fixed size, and therefore any cartridge is going to be confined to those dimensions. Simply put, the larger the overall cartridge the less magazine capacity. The larger the bullet, the less room there generally is for powder. Bigger holes are going to come at the cost of effective range. Want to shoot a .50 caliber bullet from an AR? No problem – there is definitely such a thing. Just don’t expect to go very far before hitting the ground, and don’t expect the magazine to hold 30 rounds.
Indeed, the key qualifier phrase when it comes to alternate calibers is, “…from the AR-15 platform.” None of these calibers are suddenly going to turn your AR into a big-game-African-plains-safari rifle, or lights-out-from-a-mile-away sniper platform. But they can allow you to increase ballistic performance in certain ways when shooting from the AR-15 platform, when compared to the standard 5.56 cartridge.
After reading about some of these calibers, you may find yourself asking why anyone in the civilian world would choose an AR-15 in 5.56 when it seems most of the other calibers would be more practical in most situations? The simple answer is cost per trigger pull. What fun is having a firearm like the AR if you can’t afford to shoot it the way it’s meant to be used. Because it’s a military caliber, 5.56 ammo is plentiful and reasonably cheap compared to most of the other choices.
But the real beauty of all of this is the modularity of the platform. Having to own two completely separate rifles in order to shoot two very different calibers is an obsolete concept. Everything in the AR’s lower assembly stays the same. By building a separate upper, it’s possible to go from shooting 5.56 to some other caliber and back again in mere seconds simply by swapping one upper for another. In a matter of seconds you have the best of both worlds. You’ll find this is the route many AR owners go – a rifle set up to fire .223/5.56 for range practice, and also a separate upper (or uppers) purpose-built for shooting one (or more) of the alternate calibers. No matter how many uppers you have, you can still tell your spouse that it’s only one gun, and technically not be lying! Not that I would ever do that.
With that said, let’s take a look at five of the more popular and established “alternate” AR-15 calibers readily available in the market.
300 AAC BLK
Dedicated components: Barrel
Common Bullet Weight: 120gr Supersonic, 220gr Subsonic
Pros: Shares almost all components with standard AR, cartridge options range from subsonic or supersonic, shoots suppressed subsonic very effectively, relatively short optimal barrel length (8-10 inches), widely available ammunition.
Cons: Shorter effective range. Moderate ammunition cost ($0.50 and up).
Summary: Commonly called 300 Blackout, think of it as a .308 caliber bullet stuffed into a standard 5.56mm case. It’s meant to combine the punch of an AK-47 with the superior accuracy inherent to the AR-15 platform. It can be a viable (supersonic) round for hunting or defense out to 200-300 yards. Its relatively short optimal barrel length makes it a great candidate for pistol or SBR-type setup. Availability of subsonic ammo make it ideal for use with a suppressor, which experts say has similar ballistics to the venerable .45 ACP round.
Why you might want it: Overall compactness with the option of suppressed shooting with subsonic ammunition lends itself well to defense scenarios where a high-velocity rifle caliber might be less ideal. Smaller platform can be effective and easy to maneuver in thick brush when hunting small to medium-sized game when using supersonic rounds at short to medium ranges.
Non-standard components: Barrel, Bolt, Magazine
Common Bullet Weight: 120gr
Pros: Ammunition availability and cost. Increased muzzle energy.
Cons: Not a lot of variety when it comes to hunting bullets.
Summary: Instead of coming up with a new cartridge, why not just make an AR able to shoot something that’s already widely available? Sounds like a good idea, right? The 7.62×39 is the same cartridge fired by the venerable AK-47, the most used military rifle in the world. It’s a proven hard-hitting performer on the battlefield, but it’s lack of ammo versatility hinders it as far as hunting applications are concerned.
Why you might want it: Simply put, you want to shoot cheaply and not worry about ammo supply. Up until recently this cartridge was more available and less expensive than standard .223/5.56 ammo, making it an ideal alternate choice for AR-15 owners who liked to put a lot of rounds downrange.
Non-standard components: Barrel, Bolt, Magazine
Common Bullet Weight: 123gr
Pros: Relatively strong, flat-shooting round provides more punch at longer ranges than other cartridges. Low-cost, steel-cased ammo available for cheap range plinking.
Cons: Less magazine capacity. Long barrel length needed for ideal ballistics (20+ inches). Expensive hunting/match grade ammunition. Ammunition not widely available.
Summary: The established long-range king of the AR-15, 6.5 Grendel overcomes the bullet vs powder capacity issue by using a larger diameter case at the expense of magazine capacity.
Why you might want it: The 6.5mm projectile traveling at high velocity provides much better energy on target at long-distances compared to the 5.56mm round. If you’re looking for an AR platform for hunting, the Grendel is the perfect choice. It’s effective for medium sized game out to 500+ yards, and can accurately punch paper much further.
Non-standard components: Barrel, Bolt, Magazine
Common Bullet Weight: 110gr
Pros: Good balance of muzzle energy and effective range from the AR platform. Reasonably available ammunition. Shoots well from 16-18″ barrel. Wide variety of ammunition for various applications.
Cons: Ammunition cost.
Summary: The “Goldilocks” AR-15 caliber. With the exception of a few specific shooting scenarios, it does everything pretty good.
Why you might want it: A great balance of power and effective range, relative to the platform. The shorter optimal barrel length means less length and weight, potentially making a 6.8 rifle a little nicer to carry around. Slightly less effective at longer ranges than 6.5 Grendel, but if most of your hunting or shooting is done within 400 yards, and you have no need or desire to shoot suppressed from the AR platform, the 6.8 SPC can be a good all-around choice.
.450 Busmaster, .458 SOCOM, .50 Beowulf
Non-standard Components: Barrel, Bolt, Magazine (varies), Upper Receiver
Popular Bullet Weight: 300gr – 500gr
Pros: Huge muzzle energy.
Cons: Short effective range. Magazine capacity. High-cost ammunition. Ammunition availability.
Summary: Though there are slight differences between each, I’ll present them as a group for the purposes of this article. They all accomplish the same mission, which is to turn the AR into a short-range sledgehammer, capable of putting down almost anything within 100 yards.
Why you’d want it: Short-range hunting of medium to large game. Wilderness protection against large predators. Cinder block wall penetration. Pure, unadulterated joy.
As I mentioned, these are just a few of the more popular caliber choices available. But there are many more to explore, all offering slightly optimized ballistics in some category to help you get a lot more mileage out of your AR-15.
Shooting any of the alternative AR-15 calibers is all about understanding the limitations of the specific cartridge, and implementing it accordingly. Pick the right tool for the job.
So some of the questions we’ll want to ask: Will this be the only AR caliber you plan to own? Do you plan to buy/build a separate complete upper? What other firearms do you own, and for what purpose? Will this AR be used for self or home defense? Do you want to hunt with this AR? If so, what type of hunting do you plan to do, or what types of animals do you plan to hunt? Where do you generally plan to hunt? To what degree will ammunition cost and availability play into you choice? To what degree will component cost and availability factor into your choice?
These are all questions we’ll want to investigate with you in order to make the right decision. The folks here at Next Level Armory specialize in ARs and AR builds, and we’ll be happy to help anyone find or build their ideal firearm setup. We know our stuff, because we own it and shoot it ourselves. If you’re thinking of getting into the AR world, or are an AR owner looking to extend your rifle’s capabilities, come by and talk to us today!
Be safe and happy shooting!