Rifle-length carbines

Standard AR-15 ammunition, 5.56×45mm (aka 5.56), lacks the punch of larger, heavier projectiles (bullets). Yet, it feeds the firearms of the free world. The smaller, lighter projectile begins to break apart after entering a meaty target or passing through an object. This action, called fragmentation, is one of the most important factors when considering the effectiveness, or stopping power, of the projectile. For 5.56 to reliably fragment, it needs to be traveling around 2,700 feet per second (fps).

Why a longer barrel?

For close encounters, short barrels can get the job done. But for anything beyond spittin’ range (or in this case, 100 yards), you’ll want to grab something that can get you there while maintaining a velocity above 2,400fps. A longer barrel allows for more rotations, or twists, of the projectile before it exits the barrel. More rotations will cause increased velocity at the muzzle and help to maintain it at greater distances.

At the shorter end, a barrel length of 13.7”, 14.5”, and 16” will give you just enough velocity to maintain reliable fragmentation while keeping the weight down. This weight savings can be especially important when considering the possible add-ons: a suppressor, weapon-mounted lights, laser aiming modules, and heavier optics such as Low-Powered Variable Optics (LPVOs).

If you really want to reach out and touch something (and you don’t mind hoofing the extra weight), an 18-20” barrel will maximize the effectiveness of 5.56. Even still, the likelihood of reliable fragmentation will dwindle around 200 meters. If you want to prepare for engagements beyond this distance, you might want to check out our page on large-frame ARs.