The Best AR15 Deer Hunting Calibers, Compared

Yes, you can hunt with an AR-15 in most U.S. states. The AR platform is excellent for building a lightweight, accurate hunting rifle that can easily be configured to adhere to some states' hunting restrictions on magazine capacity and calibers. Unlike most bolt guns and deer rifles -- which need to be bought off the store shelf as-configured -- you can easily build a custom AR-15 in any caliber to better suit your needs in the field. Just pick the right barrel and bolt for your new or existing AR, install them both (here's how to do it), and you're ready to take game.

Best Deer Hunting AR15 Calibers

So, which AR-15 calibers are the best for hunting? Let's start with the obvious: Deer calibers.

6.5 Grendel

• Bullet Diameter: 0.264"
• Case Length: 1.52"
• Overall Length: 2.26"
• Case Capacity: 35 gr. H2O
• Twist Rate: 1:8, 1:9
• Common Weights: 90 to 130 grains

When it comes to hunting deer with an AR-15, 6.5 Grendel is, by far, the most popular caliber. It offers low felt recoil and has a nearly flat trajectory within 200 yards, making it a breeze to land trophies with. It offers ample takedown power for any deer, especially when chambering 120- to 130-grain loads.

Even chambered in a barrel as short as 16", 6.5 Grendel offers more than enough energy for deer, and its OTM and HP loads will reliably expand to ensure a quick and humane kill. It's this point that drives home why 6.5 Grendel is arguably the most popular AR-15 deer caliber: It offers superior performance over most other deer cartridges, with high takedown power in a lighter rifle that offers laser accuracy, and it does all this with little more than a gentle nudge to the shoulder with each trigger pull.

For the best performance against deer, stick with 120-grain loads -- it offers the best balance of velocity, bullet drop, and energy -- and use a 1:8 twist rate.

6mm ARC

• Bullet Diameter: 0.243"
• Case Length: 1.49"
• Overall Length: 2.26"
• Case Capacity: 34 gr. H2O
• Twist Rate: 1:7, 1:7.5
• Common Weights: 80 to 108 grains

6mm ARC is becoming a top contender for deer hunting with the AR-15, and it's even now being cited as a better option than 6.5 Grendel. While offering nearly the same energy and takedown power as 6.5 Grendel, 6mm ARC offers even less felt recoil and even flatter trajectories.

In other words, you're getting the same lethality while taking even more accurate shots. Like 6.5 Grendel, 6mm ARC can be chambered in a short configuration with a 16" barrel and provide all the accuracy and lethality needed to take deer within 200 yards with ease.

The most popular 6mm ARC load for deer is Hornady's 103-grain ELD-X, which offers an incredible ballistic coefficient (0.512, G1) and a muzzle velocity of more than 2,400 FPS in a 16" barrel, allowing it offer performance with virtually zero drop and no holdovers required within antler-taking range. For this load, stick with a 1:7.5 twist rate.

6.8 SPC

• Bullet Diameter: 0.277"
• Case Length: 1.68"
• Overall Length: 2.26"
• Case Capacity: 34.8 gr. H2O
• Twist Rate: 1:9.5, 1:10, 1:11, 1:12
• Common Weights: 90 to 120 grains

Some argue that, when taking deer, a wider cartridge is more forgiving when it comes to shot placement and tracking distance after a hit. Enter 6.8 SPC: This .277-caliber load is the answer, with many hunters favoring it for its wider diameter and potentially more effective expansion.

6.8 SPC has become such a popular deer caliber that it's now available under Winchester's Season XP line as a 115-grain load, which promises more rapid and reliable expansion on impact.

6.8 SPC also provides slightly less felt recoil than 6.5 Grendel, with most saying it's more comparable to 6mm ARC's felt recoil. Despite its loser sectional density, 6.8 SPC still offers high ballistic coefficients across its various loads and, therefore, it affords the flat trajectory any hunter desires when taking deer within 250 yards.

Above all else, 6.8 does so well as an AR-15 deer caliber because of its powder and loads: Across nearly all grain weights, it'll achieve more than 90% of its nominal velocity in a 16" barrel. When chambered in a 24" barrel, for example, 110-grain loads will produce a muzzle velocity of 2,750. Drop down to a 16" barrell, and it'll still produce 2,550 FPS.

Its this performance in shorter barrels that makes 6.8 the perfect cartidge to pair with the AR-15, allowing you to enjoy hunting with a compact setup.

.350 Legend

• Bullet Diameter: 0.357"
• Case Length: 1.71"
• Overall Length: 2.25"
• Case Capacity: 36.5 gr. H2O
• Twist Rate: 1:10, 1:16
• Common Weights: 145 to 255 grains

Some states require that hunters use a caliber at least 0.35" in diameter when hunting deer. Others require the use of straight-walled casings. So, it should come as no surprise that the straight-walled .350 Legend has become yet another popular deer caliber for hunting with the AR-15, offering a solution for both restrictions.

Despite its straight-walled casing and high powder capacity, .350 Legend offers surprisingly low felt recoil with intermediate velocity and power, producing over 2,200 FPS and 1,600 ft-lbs. of energy at the muzzle for the common 145-grain load when fired from a 16" barrel.

That last bit matters: Like our other top hunting calibers, .350 Legend produces nominal velocity and energy in the minimum legal barrel length of 16", making it an ideal cartridge for the AR platform, and it retains more than enough power to reliably take down game at up to 200 yards.

.450 Bushmaster

• Bullet Diameter: .452"
• Case Length: 1.7"
• Overall Length: 2.26"
• Case Capacity: 59.5 gr. H2O
• Twist Rate: 1:16, 1:24
• Common Weights: 245 to 395 grains

The .450 Bushmaster cartridge was specifically designed in 2007 for the AR-15 platform, with the sole intent of being able to take down American big game with one shot at up to 250 yards.

With 250-grain loads producing over 2,100 FPS and more than 2,500 ft-lbs. of muzzle energy in a 16" barrel, the .450 Bushmaster is capable retaining over 1,000 ft-lbs. of energy at 250 yards, the number oft cited as the minimum amount of energy to reliably take game.

Although not quite powerful enough for brown bear, hunters have for more than a decade fielded .450 Bushmaster to take down elk and black bear aplenty. Thanks to its straight-walled casing, .450 Bushmaster is a yet another great alternative for hunters living in locales with restrictions on bottlenecked cartridges.

Despite its weight and relatively low velocities, .450 Bushmaster shoots quite flat within typical game-taking distances, and its ballistics offer no-guess points of aim. Many hunters employ a 175-yard zero that offers about 2.5" of rise at 100 yards, and 2.5" of drop at 200 yards. This effectively keeps points of impact within the kill box for American game and requires no holdovers when taking shots between these distances.

Despite qualifying as a bona fide "big bore" load, .450 Bushmaster still offers manageable felt recoil -- just 20% more than .308, depending on the load comparison -- and it can be easily tamed further when paired with the right brake.