All the Calibers an AR-15 Can Shoot
One of the most appealing aspects of the AR-15 platform is its modularity. Unlike traditional rifles that are locked into a single chambering, the AR-15 can be converted to fire a wide range of calibers by swapping out the upper receiver, barrel, and sometimes the bolt carrier group. This versatility has made the AR-15 one of the most popular and adaptable firearms in the United States.
In this guide, we cover all the major calibers an AR-15 can shoot, from the standard military cartridges to popular hunting rounds and specialty options.
The Standard: .223 Remington and 5.56x45mm NATO
The AR-15 was originally designed around the .223 Remington cartridge, which is closely related to the military 5.56x45mm NATO round. Most AR-15s sold today are chambered for one of these two cartridges, and they can be used somewhat interchangeably with an important caveat: a rifle chambered for 5.56 NATO can safely fire both 5.56 and .223, but a rifle chambered strictly for .223 Remington should not fire 5.56 NATO, as the higher pressure of the military round can cause issues.
These cartridges offer excellent accuracy, flat trajectory, and manageable recoil, making them ideal for target shooting, varmint hunting, and home defense.
Popular Alternative Calibers
.300 Blackout (7.62x35mm)
The .300 Blackout was developed to provide a heavier projectile in the AR-15 platform while using the same bolt and magazine as the standard 5.56 configuration. Only the barrel needs to be swapped. It is widely used for suppressed shooting and is effective for deer-sized game at close to moderate ranges.
6.5 Grendel
The 6.5 Grendel was designed to extend the effective range of the AR-15 platform significantly beyond what the 5.56 is capable of. It uses a modified bolt and magazine but fits in a standard AR-15 lower. Shooters use it for long-range target shooting and medium to large game hunting out to several hundred yards.
6.8 SPC (6.8mm Remington Special Purpose Cartridge)
The 6.8 SPC was developed by the U.S. Army Special Forces to offer improved terminal performance over the 5.56 at short to medium ranges. It is popular for hunting hogs and deer. It requires a dedicated bolt, barrel, and magazines.
.350 Legend
The .350 Legend is a straight-walled cartridge designed for deer hunting in states that restrict hunting to straight-walled calibers. It fits in a standard AR-15 lower with a modified upper, bolt, and barrel. It provides effective terminal performance on deer-sized game at ranges up to 200 yards.
.224 Valkyrie
Federal Premium developed the .224 Valkyrie to deliver superior long-range performance compared to the 5.56, using a heavier, high-BC bullet that stays supersonic out to 1,300 yards. It requires a new barrel, bolt, and magazines but uses the same lower receiver.
9mm and Other Pistol Calibers
AR-15 pistol caliber carbines (PCCs) chambered in 9mm are increasingly popular for competition shooting, home defense, and range use. A 9mm AR-15 uses a dedicated upper receiver and barrel along with a magazine adapter or different lower to accept pistol magazines. The result is a soft-shooting, affordable-to-feed rifle with reduced noise and recoil.
Other pistol calibers available for AR-15 builds include .40 S&W, .45 ACP, and 10mm Auto.
.458 SOCOM and .50 Beowulf
These large-bore calibers are designed for maximum stopping power at close range. The .458 SOCOM and .50 Beowulf both fit in a standard AR-15 lower but require dedicated upper receivers. They are popular for hog hunting, dangerous game, and specialty applications where hard-hitting performance at short range is the priority.
Rimfire Conversions: .22 LR
While not a true caliber swap, .22 LR conversion kits allow shooters to fire rimfire ammunition through an otherwise standard AR-15. These kits replace the bolt carrier group and magazine and allow for inexpensive practice with the same manual of arms as the centerfire version. Dedicated .22 LR upper receivers are also available for a more complete conversion.
Which Caliber Is Right for You?
The best caliber for your AR-15 depends on what you intend to do with it:
- Target and range shooting: .223/5.56 or .224 Valkyrie
- Suppressed shooting: .300 Blackout
- Long-range hunting: 6.5 Grendel or .224 Valkyrie
- Deer and hog hunting: 6.8 SPC, .350 Legend, or .300 Blackout
- Hard-hitting close range: .458 SOCOM or .50 Beowulf
- Affordable practice: .22 LR conversion
- Low recoil competition: 9mm PCC
No matter which caliber you choose, the AR-15 platform provides the flexibility to build a dedicated upper for each purpose while sharing the same lower receiver. That modularity is one of the core reasons the AR-15 remains America's most popular rifle. If you are looking to purchase your first AR-15 or add a new upper to your collection, use FFL Search to find a licensed dealer near you.