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Five AR-15 Calibers for Hunting Deer

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AR-15 and AR-10 style are an increasingly popular choice for the modern hunter, and it’s easy to understand why: the modern sporting rifle is the most popular rifle in the nation, and gun-owners want to get the most from their favorite rifles.

As the popularity of the platform has increased, so has the demand for powerful new cartridges that provide marksmen with the performance needed to drop deer.

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Today, we are breaking down our favorite AR-15 and AR-308 calibers that will help you bag that buck, whether you’re sitting in a tree stand, perched in a blind, or stalking muleys over hill and dale. This article will have the perfect cartridge for any environment or any distance, so you can be confident that you’ve made the right choice for the next hunting season.

Which one will help pack your freezer with fresh venison this year? Let’s dive in.


The AR-15 is one of the most versatile rifle platforms on the planet, host to countless cartridges, both common and niche. Fortunately, for hunting, you won’t need to search hard for a good option.

AR-15s are one of the most popular hunting rifles in America nowadays, and there are several effective, accessible calibers with bustling aftermarkets. These cartridges include 6.5 Grendel, .300 Blackout, .450 Bushmaster, and .350 Legend.



The 6.5 Grendel cartridge was designed in part by Bill Alexander of Alexander Arms, and the goal of the project was to create a round for the AR-15 that had a superior ballistic coefficient and terminal performance than .223 Remington or 5.56 NATO.

Grendel projectiles can be up to twice as heavy as standard 5.56 NATO rounds, and can reach velocities of around 2500 fps, all while shooting relatively softly for the power it’s packing. The 6.5mm bullet is long and thin, giving it excellent wind bucking abilities that can deliver a punch with almost double the kinetic energy than a .30-30 at 300 yards.

Much beyond that distance, terminal energy drops below 1000 foot-pounds, and the terminal effectiveness (and morality) of the shot dips hard. If you’re the guy or gal in a blind or tree stand, chances are good the Grendel will fit your needs perfectly.

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There are some things to consider if you choose 6.5 Grendel as your new deer hunting round.

6.5 Grendel comes in two flavors: Type I and Type II. As you might have guessed, components that work with one type are potentially dangerous to mix with use of the other type.

The good news is that Type II has become the most widely used version and is more than likely what most people are referring to when they say “6.5 Grendel.” But it is still important to verify compatibility and part type when building for this caliber.

If you’re looking to convert a .223 Remington or 5.56 NATO AR-15 into a 6.5 Grendel deer rifle, all you need is a new bolt carrier group, a barrel, and some 6.5 Grendel magazines.

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A popular choice for many hunters that hunt with their ARs is to build a dedicated 6.5 Grendel upper and swap that out for their standard .223/5.56 upper when deer season comes around. The modularity of the modern sporting rifle makes it easy and convenient to quickly turn the one rifle you already have into two.

300 blackout


The .300 Blackout cartridge has grown wildly in popularity since it hit the shelves in 2011.

Like the 6.5 Grendel, .300 BLK was originally designed to fit a specific need for the U.S. Military. .300 Blackout maximizes the performance of a suppressed carbine rifle. Advanced Armament Corporation started with the .300 Whisper wildcat cartridge and made some minor modifications, allowing the round to fit double-stacked in standard AR-15 magazines.

To achieve the military’s demands, .300 BLK used 220 grain bullets for subsonic performance. This made .300 BLK one of the quietest practical cartridges when combined with a suppressor. For further engagements, the lighter supersonic loadings proved quite effective, reaching speeds of around 2200 feet per second with 125-130 grain bullets.

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It’s not a ‘high velocity’ round by any means, but a 30-caliber bullet from an AR-15 rifle is certain to draw attention. To no surprise, it quickly became one of the most popular AR cartridges in the US.

The Blackout has a lot going for it, but it has limitations as well.

The .300 BLK casing is essentially the same dimensions as .223 Remington brass, trimmed down and necked to accept the 30-caliber bullet. This means considerably less room for powder. Blackout burns through its propellant in about roughly a 10-inch barrel, making it popular for the SBR and AR Pistol crowd, but it also means it loses velocity much faster than other 30-caliber cartridges.

Because of this, you’re going to be limited to much shorter ranges to be effective enough to hunt deer. Now, if you’re the hunter up in the hardwood forests sitting in a tree stand or a ground blind where most shots taken are under 75 yards, you’ve got nothing to worry about.

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In fact, I would dare to say you’re in luck. The supersonic loadings that many manufacturers are offering in .300 BLK pack a serious punch. Moving faster than their subsonic, suppressor-friendly counterparts, quality .300 BLK hunting ammunition like the Barnes VOR-TX 110 grain round can expand to twice the diameter of the bullet upon impact.

The result is a wider wound channel, which effectively and ethically puts down deer-sized game. While the heavier weights of subsonic loads might seem advantageous for taking game, these rounds are just moving too slow to expand enough and be reliably lethal.

The number one advantage of the 300 Blackout is how versatile it makes the AR-15 platform. All you need to take your AR-15 from a .223/5.56 plinker to a deer-dropping hunting rifle is a .300 Blackout barrel.

.300 Blackout uses the same bolt, same magazines, and same lower receiver as your standard MIL SPEC AR-15. Just like with Grendel, a popular way to turn one rifle into two is to just build a dedicated 300 Blackout upper and swap it out when you need it.



First idealized in concept by Lt. Col. Jeff Cooper, whose contributions to the firearms community are hard to overstate, the “thumper” concept lives on today in a handful of calibers for the AR-15 platform. One such caliber is the .450 Bushmaster, and we think it makes for a fantastic deer hunting cartridge.

Cooper’s dreams of a “thumper” came with some stipulations. Whatever type of rifle was going to fit the Thumper concept had to be big bore, so .44-caliber or larger. He also envisioned it being semi-automatic, lightweight, and capable of one-shot takedowns on large game at 250 yards and closer.

Bushmaster Firearms was given the license to Tim LeGendre’s “.45 Professional” cartridge and, working with Hornady, made some slight modifications to create .450 Bushmaster.

It’s not difficult to understand the potential benefits of a big bore caliber in an AR-15, and Bushmaster packs the hard-hitting performance to boot. High quality factory loadings from leading ammunition manufacturers can attain muzzle velocities around 2200 fps with a 250-grain bullet that’s still packing 1250+ foot/pounds of energy at 200 yards.

That’s a lot of thump.

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A significant benefit of the Bushmaster over the other limited number of big bore options for the AR-15 is the fact that it uses a straight-walled casing. In many regions around the country, hunting in “limited firearm zones” means there are strict rules about the types of ammo you can use to hunt deer.

In my home state of Michigan, as an example, the southeastern region of the state was once restricted to shotguns and muzzleloaders only. In 2014, the regulations were changed to include .35-caliber or larger straight-walled cartridges with a case length between 1.16 and 1.80 inches.

This still eliminated popular big bore options like .45-70 Government lever action rifles but leaves the door open for cartridges like .450 Bushmaster, which deliver similar performance at appropriate ranges and can be fired from the AR you already have with a dedicated .450 upper receiver.

To equip your AR-15 to shoot .450 Bushmaster, the bare essentials you will need are a .450 bolt, and a .450 Bushmaster barrel.

It’s also likely that you’ll need to have your upper’s ejection port opened up a small amount. We suggest having a gunsmith do that for you unless you’re very experienced with gunsmithing yourself.

As with the previous calibers, many marksmen will build a dedicated upper receiver to swap onto their lower when it’s time to hunt.

The limitations of the cartridge are also obvious. In a short action rifle with the size limitations of the AR-15, pushing a 250-grain projectile with any considerable speed is nothing short of a feat of engineering. But the Bushmaster’s ballistic coefficient does mean that when the round starts slowing down, it slows down fast. While many loadings today carry enough energy to ethically take a deer at 300 yards with .450 Bushmaster, the bullet will have dropped about 40 inches at that distance.

Again, most hunters are sticking within 100 yards, so unless you hunt on the prairies, .450 deserves a place in your arsenal.

.350 Legend

The newest addition to our list of top hunting cartridges is .350 Legend.

This purpose-designed hunting cartridge is only a few years old, but hunters around the country are praising its effectiveness in the field. Having used this cartridge in our own rifles, we share their enthusiasm.

This cartridge does a lot that you won’t find in older cartridges, translating to improved performance for the hunters who want every advantage.

.350 Legend is the fastest straight-walled cartridge in the world, offering more energy than .300 Blackout or .223 Remington while reducing recoil compared to big-bore cartridges. Winchester says it gives better penetration and less recoil than .243 Win, which is a compelling statistic on its own.

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Winchester developed this cartridge for deer hunting specifically, so it released with a wide variety of quality hunting ammo already available. The only downside is that, as a new cartridge, parts and ammunition might be less accessible.

Fortunately, it’s easy to build a .350 Legend rifle. This cartridge uses a .223 case, so it is compatible with all standard AR-15 bolt heads and magazines. All you need is a new barrel, and you can convert your standard rifle into a .350 Legend.

If you care about getting the absolute most from your hunting rifle, .350 Legend is a good choice.

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If you want something that hits a little bit harder, why not step it up to an AR-10.

The older and larger brother of the AR-15, the AR-10 is compatible with full-power rifle cartridges, which have dominated the hunting world for over a century. While it may look different from your grandfather’s bolt gun, the AR-10 is every bit as reliable and practical in the field.

If you’re considering a new AR10 or AR308 build for hunting, consider one of these two calibers. They’re among our favorites on the market, and they’ll do you well on the hunt.



The granddaddy of them all. .308 is arguably the most popular short-action hunting cartridge for large game in the world, and for good reason.

The .308 Winchester has stood the test of time. Not much has to be said about the .308’s effectiveness on the hunt—it has over half-a-century’s worth of trophies on the buck pole to prove its merits. It’s also the parent case to many cartridges that have seen success for hunters over the decades, such as the .243 Winchester and the venerable 7.62X51mm NATO.

.308 Winchester is based on the older .300 Savage and designed for semi-automatic effectiveness, supplanting the .30-06 in en-bloc magazines used by American servicemen carrying the M1 Garand during WWII.

The .308 has certainly got history on its side, and it is growing again in popularity because of the commercial success of DPMS pattern AR-10 style rifles. With a longer chamber, larger bolt head, and all the modularity and versatility of a modern sporting rifle platform, the AR-10 has become a hunter’s dream.

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The .308 Winchester pushes the modern sporting rifle’s capabilities well beyond the limits of the smaller calibers of the AR-15. Factory loadings for the .308 Winchester range in weight from 125-grain to 220-grain subsonic loads. The cartridge’s popularity also means plenty of information and hardware is easily accessible for hand-loaders who want custom-tailored, high-performance loadings that really push the limits of the Winchester’s capabilities.

From the factory, a match grade 168-grain load will pack more than 1000 foot-pounds of energy out to about 600 yards or so out of a 24” barrel. That’s well beyond the limits of any AR-15 hunting cartridge.

So, if you’re the hunter out on the plains or up in high country who may need to be ready for a long shot, consider stepping up to the AR-308 platform.


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The .308 Winchester is not a young cartridge. If you are looking for the most modern design, look elsewhere. That said, many have tried to challenge the Winchester over the half-century since its introduction, yet none has cast it down. It is not hard to imagine that, in the 22nd century, .308 will remain a prominent cartridge for hunters across America.

Not that there is no competition. In the last decade, one cartridge has grown in prominence, and many call it the ‘replacement’ for .308 Winchester. That cartridge is, of course, 6.5 Creedmoor.

Will that prediction come true? Only time will tell.


The 6.5 Creedmoor was born not of wartime necessity, but from the dreams of long distance marksman Dennis DeMille, and the ballistics knowledge of Dave Emary, senior ballistician at Hornady Manufacturing.

DeMille, a high-power rifle shooting champion, was lamenting the inefficiencies of commonly available high-power ammunition and his reservations with hand-loaded wildcat cartridges that were becoming so widely used among high-power, long-distance competitors.

The Creedmoor was purpose-built to be unmatched in its long-range potential, and after a few years of victories, this cartridge has become a fan favorite.

The cartridge designers chose 6.5mm because of its proven ballistic efficiency and high sectional density. The casing is based on the .30 Thompson Center cartridge, which was itself based on the .308 Winchester. So, you could say with some degree of accuracy that the Winchester is the granddaddy of 6.5 CM. If nothing else, Creedmoor certainly stands on its shoulders.

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Creedmoor took off with long-range competitors in the late 2000s. Within a few years, however, hunters took note as well.

Creedmoor outperforms .308 in all but a few categories. The Winchester has a higher initial velocity—from the muzzle out to about 100 yards—and more energy until about 300 yards, at which point, the more efficient 6.5mm bullet beats it.

But the real benefit of the Creedmoor is how flat it shoots and how well it handles crosswind at long distance. In a 10-mph full value cross wind at 500 yards, the .308 Winchester has been pushed about 6 inches further off target than the Creedmoor. Out to a thousand yards, that difference is more about 45-50 inches.

For the long-distance hunter, or the hunter who just wants a fast, flat-shooting cartridge for their AR-10, the Creedmoor shines.

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Did you find the right cartridge for your next right?

Hopefully, this article has been helpful in guiding you onto the right path for a quality hunting AR15 or hunting AR10.

Make no mistake, all the hunting rounds discussed here today will get the job done—and there are more still that reliably harvest deer for hunters every year. It’d be close to impossible to compile a complete list of every bullet that can down a buck.

The cartridges in this article are proven solutions that make the most out of the versatile modern sporting rifle, and if you’re looking to hunt deer this year with your favorite AR, then you cannot go wrong with any of these choices.

We wish nothing but safety and the best of luck to all the hunters out there who will be putting meat on their family’s table and trophies on their walls this season.

Best of luck to you on the hunt!