The AR platform isn’t only the most highly customizable rifle platform on the market, it’s probably the most diverse when it comes to calibers. This is a platform that’s available in practically endless chamberings from diminutive 22 LR to hard-hitting 450 Bushmaster. Whatever you intend to do with your AR-15 or AR-10, there’s a caliber for you. We’re going to help you narrow down the caliber of your next AR by listing our top 5 picks, and what they’re ideal for.
6.5 Creedmoor
Let’s just get this one out of the way. Like it or not, 6.5 Creedmoor is a great long-range round that’s more than proven itself both at the range and on hunts. It produces a flatter trajectory than many cartridges are capable of, it’s accurate on target, and it’s widely available. There’s a lot to be said for availability, too, because the last thing you want is a rifle or chambering that isn’t easy to get parts or ammo for.
The 6.5 Creedmoor is an AR-10 platform round, meaning you’re not going to find it in the lighter-weight AR-15. Even so, you can find it in carbine-length guns and relatively light options. It’s great for hunting pests, varmints, predators, and mid-size game animals and it excels at ringing steel at significant distances. 6.5 Creedmoor is a truly versatile cartridge and it’s well worth having at least one AR-10 chambered in it in your collection.
6mm ARC
Want a flatter shooting round, but don’t want to commit to the heavier AR-10? You’re in luck because the 6mm ARC is that round. Hornady designed this cartridge to outperform many — most — others in its category, and all in an AR-15. That means a lighter rifle but one that can still nail shots at longer ranges. The 6mm ARC’s parent cartridge is the 220 Russian and it has a bullet diameter of 0.243 inches. Its overall length is 2.260 inches. Generally speaking, its effective hunting range is about 500 yards, but that’s both game-specific and affected by the ammunition being used.
This isn’t just a hunting round, though. In fact, it was adopted for use by a special forces group before it even hit the market for the general public. Testing shows a far superior performance to the classic 5.56 NATO round. The 6mm ARC is a great choice for home defense rifle or truck gun use. Its close-quarters use is also impressive — it isn’t relegated to long-range only — and it’s quite precise. 6mm ARC doesn’t have quite the reach of 6.5 Creedmoor but it provides stellar results from the AR-15 platform and is definitely the longer-range star of the AR-15 show.
450 Bushmaster
If you’re thinking that the 450 Bushmaster has a tendency to drop like a brick beyond 100 yards, you’re not exactly wrong. However, it’s still an excellent round for closer-range use. The 450 Bushmaster has a bullet diameter of 0.4520 inches and an overall length of 2.260 inches (yes, it’s the same length as 6mm ARC, just with a way bigger bullet). The creation of this cartridge is largely credited to the late Col. Jeff Cooper, although he isn’t the person who actually designed it — he just wanted a “Thumper” round. Credit goes to Tim LeGendre of LeMag firearms, who came up with the initial design that was then tweaked a little by Hornady (with LeGendre’s permission).
450 Bushmaster delivers impressive energy transfer. With a 250-grain bullet, it produces almost 3000 foot-pounds of energy at the muzzle, and the resulting impact within 100 yards creates an enormous wound cavity. Of course, if you’re just shooting steel, it’s great for that as well. There’s nothing quite like a big bore AR, and the 450 Bushmaster is a big bore that’s here to stay.
This is a cartridge with enough ready availability to be handloaded and also built if you prefer building your own AR. Its effective range is generally considered 150 yards but the actual drop rate depends on the specific load being used. You might find yours doesn’t drop quite as precipitously. Just familiarize yourself with it before you use it for hog or coyote hunting. If you’re using it for home defense, just be sure you know how it penetrates and adhere to the rules of safety and responsibility for every shot fired, just like you would with any other caliber.
300 Blackout
The reason for including 300 Blackout is that it’s a purpose-driven cartridge created for close-quarters use. If your goal in building or buying an AR-15 is home defense, or even to have a good truck gun on hand, the 300 Blackout is a logical choice. It’s not going to reach out and touch distance targets, but it doesn’t need to do that. 300 Blackout was designed in 2009 by AAC (Advanced Armament Corporation) for close-quarters battle (CQB). As a matter of fact, it was and is meant to perform its best using subsonic rounds through a suppressor.
300 Blackout has a 0.308-inch bullet diameter and an overall length of 2.26 inches. Significant drop begins after 100 yards, so while it’s certainly possible to ring steel with this round at longer distances, it doesn’t have a great effective range for hunting or defensive use. But it’s ideal for an AR-15 you keep around for home defense at the standard house-size defensive ranges. Even better, it’s fantastically quiet when you run it suppressed, so we highly recommend investing in a tax stamp to get a suppressor on your 300 Blackout. If you can pair that with yet another tax stamp for a short-barreled rifle (SBR), you won’t be disappointed.
Side note: For the crowd undoubtedly claiming 300 Blackout is a great hunting round, well, it’s not. Although it can get the job done on smaller game at close enough ranges, it isn’t ideal for feral hogs or game like deer. Some cartridges are meant for a precise niche, and this is one of them. Close quarters? Get yourself a 300 Blackout. Want longer-range shots? Look elsewhere.
308 Winchester
This one’s an AR-10 classic we can’t resist including. 308 Winchester has been around since 1952 and as time has gone by it’s enjoyed all the benefits of advances in technology while maintaining its versatility. The 308 Win cartridge was released by Winchester right before the military version — 7.62x51mm NATO — was accepted as a service cartridge. The two rounds are extremely similar but do have some slight differences. 308 Win is great for everything from plinking to shooting steel to self-defense to hunting. There are even 308 Win handguns (yes, really).
Whatever you want your 308 Win to do, it can do it. This cartridge is capable of fantastic precision and is good for truck guns, home defense guns, and hunting. It’s widely available and there are a ridiculous number of 308 Win loads, thanks to its longevity and popularity. No, it doesn’t have quite the reach as 6.5 Creedmoor, but it remains a solid option. Some shooters like it because it’s a classic while others are just pleased with its results on target. The 308 Winchester is not unlike the 223 Remington. It’s a round you kind of have to have in your collection (only it’s more useful than the 223 Remington).
What are your favorite AR calibers? Tell us in the comments.
