Which Caliber Option is Right for Your MSR?
Modern Sporting Rifles are increasingly being made in calibers other than the original AR-15’s chambering of .223 Rem. Today you can plink with them, hunt with them, and defend your home with them.

The rise in the popularity of MSR rifles has resulted in new models chambered for a variety of calibers. Whether you’re a hunter, competitive shooter or general enthusiast, you can find an MSR to fit your needs. Here are some of the most popular chamberings today, and what it offers shooters:

.22 LR

The all-American .22 Long Rifle is the perfect beginner or training cartridge, since it produces very low recoil and not much in the way of muzzle blast. The mild .22 is a great way to introduce new shooters to the MSR platform and works well on varmints and pests at close range.

.204 Ruger

The .204 Ruger cartridge, which is based on the .222 Remington Magnum, drives a 32-grain bullet at 4,225 feet per second, making it one of the flattest-shooting varmint cartridges ever designed. It’s also extremely accurate and an excellent choice for varmints and predators all the way out to 300 yards.

.223 Remington/5.56 NATO

A huge selection of .223 and 5.56 ammunition is available, and shooters can find just the bullet they are looking for, whether for competition, marksmanship training, or hunting. In addition, this caliber is just about perfect for varmints, small predators, and coyotes.

.243 Winchester

This is one of the most popular and versatile hunting cartridges on the market. Loaded with bullets weighing 80 grains or less it is a fantastic varmint and predator cartridge, but with heavier, tougher bullets, it makes an excellent deer and antelope round.

6mm Creedmoor

The 6mm Creedmoor is relatively unknown outside of long-range shooting circles, but it is both an accurate and potent cartridge. It can propel 100-grain bullets at over 3,000 feet per second, and it benefits from a wide range of available .243/6mm bullets.

6×45 (6mm-223)

This .223 Remington is necked up to accept 6mm/.243-inch bullets and works well in MSR rifles. It’s a mild-recoil round with a boost in power over the standard .223, and is a much better deer cartridge than its parent cartridges, though the effective range for deer-size game is about 150 yards. It’s an excellent varmint-hunting cartridge, pushing a 75-grain bullet in the neighborhood of 2,700 feet per second.

25-45 Sharps

The Sharps Rifle Company’s 25-45 Sharps cartridge is fully compatible with .223 /5.56 bolts and magazines. All that is required to swap your existing .223 to the 25-45 is a barrel change. The new 25-45 pushes an 87-grain bullet at 3,000 feet per second, providing a significant boost in energy over the .223 for hunting deer, antelope, and hogs.

6.5 Creedmoor

The Creedmoor is based on the necked-down .30 TC cartridge and has quickly become a favorite among long-range shooters and hunters. Hornady factory loads push a 120-grain bullet at over 2,900 feet per second. Using this round also means firing long, aerodynamic .264-inch bullets that do a great job bucking the wind. It’s large for varmints, but it’s a fantastic round for deer-size game.

6.5 Grendel

Bill Alexander’s 6.5 Grendel, which debuted back in 2004, has gained quite a following among long-range MSR shooters, thanks in large part to the fact that 6.5mm bullets possess a high ballistic coefficient for better long-range accuracy. With 123-grain Hornady SST bullets leaving the barrel at just under 2,600 feet per second, this is an effective long-range hunting round for deer, antelope, and the like.

6.8 Remington SPC II

The 6.8 fires .277-inch hunting bullets in weights from 80 to 120 grains. This is a solid varmint cartridge and works well on deer-size game at moderate ranges, but velocity and energy begin to drop sharply after a couple hundred yards.

.300 Blackout

The Blackout is available in bullet weights from 110 to 220 grains, but the larger bullets are subsonic and don’t perform as well on game as the 110-125 grain loads. With velocities ranging from about 2,200 to 2,400 feet per second in these weights, the Blackout makes an excellent varmint and deer cartridge within 300 yards.

.308 Winchester

The .308 Winchester is by no means a new cartridge, but it is nonetheless an effective varmint and big-game round. Because it requires a large platform, rifles will be heavier than those for smaller cartridges, but this is one of the most versatile cartridges on the market for anything from varmints to big game.

.300 Winchester Magnum

There’s no big game in North America (and very little in the world) that you can’t take with the popular and time-tested .300 Winchester Magnum. If you’re looking for the ultimate long-range big-game MSR cartridge, this is it, but you’ll pay a premium to have an AR in this caliber.

.338 Federal

Based on a necked-up .308 Winchester, the .338 Federal will do everything that its parent cartridge will and then some. With bullets weighing from 185 to 210 grains, it packs more punch than the .308 for big game, like elk and moose, and will stop an angry bear in a pinch.

9mm Luger

The 9mm isn’t a big-game cartridge, but it’s fun to shoot and will work on varmints and pests at close range. If you’ve got a 9mm pistol, it’s nice to have an MSR that shoots the same rounds. The added velocity gleaned from a longer barrel also makes this an ideal self-defense MSR.

.450 Bushmaster

The .450 Bushmaster fires 250- to 275-grain bullets between 2,100 and 2,200 feet per second, making it an excellent close-range round for pigs and deer-size game. The .450 is a good choice for anyone who wants to pursue big game at moderate ranges or in heavy cover. It hits with enough authority to drop even the biggest, toughest hogs, and it’s an ideal cartridge for hunting black bears over bait.

.458 SoCom

The SoCom is available in bullet weights from 250 to 500 grains, but bullets in the 250- to 350-grain range with velocities from 1,750 to about 2,000 feet per second are the most effective for big-game hunting. The SoCom is a close-range cartridge, but it is very effective on game such as wild pigs, black bear and deer.