AR-15 Barrels

Barrel Length: 16", 18", and 20"

Barrel length affects velocity (approximately 25–50 fps per inch), maneuverability, and legal classification. 16″ is the standard minimum barrel length for a rifle-configuration AR-15—barrels shorter than 16″ require NFA registration as a short-barreled rifle unless the firearm is configured as a pistol. 16″ is the most versatile all-around length, providing adequate velocity for defensive and hunting use with a practical overall length. 18″ adds meaningful velocity for longer-range precision use and competition. 20″ replicates the original M16 length with maximum velocity from 5.56, favored by precision competition shooters running Mk262-equivalent loads. For pistol-configuration AR builds, 10.5″ and 11.5″ are the most common short barrel lengths. See also: AR-15 Rifles and Short Barrel Rifles.

Caliber: 5.56, .223 Wylde, .300 Blackout, and More

Most AR-15 barrels are chambered in 5.56 NATO, which safely fires both 5.56 NATO and .223 Remington ammunition. .223 Wylde is a hybrid chamber that provides slightly better accuracy than a standard 5.56 chamber while still accepting both 5.56 and .223 Rem—popular on precision builds. .300 Blackout (7.62x35mm) is the most popular caliber conversion, requiring only a barrel change to convert a 5.56 lower into a platform that fires supersonic and subsonic .30 caliber loads—the latter being the quietest suppressed centerfire option available. Other common caliber conversions include .224 Valkyrie for long-range performance and .22 LR conversion barrels for affordable training. See also: .300 Blackout Ammo.

Twist Rate: Matching Bullet Weight

Barrel twist rate determines which bullet weights stabilize properly in flight. In 5.56/.223, 1:9 twist works well for 55-grain bullets. 1:8 is the most versatile option, stabilizing common bullet weights from 55 to 77 grains and recommended for most builders. 1:7 handles the heaviest match bullets (77–90 grain) and is the military standard twist for M855 and M855A1 ammunition. For a general-purpose defensive or hunting AR-15 build, 1:8 is the standard recommendation. For a dedicated precision build running heavy match bullets, 1:7 or 1:8 are both appropriate depending on the specific bullet.

Chrome-Lined vs. Stainless: Durability vs. Accuracy

Chrome-lined chrome-moly barrels are the military standard—chrome lining provides superior corrosion resistance, longer service life under sustained fire, and resistance to erosion from neglect. They are the right choice for a defensive rifle that may experience irregular maintenance schedules. Stainless steel (416R) match barrels machine to tighter tolerances and produce smaller groups in precision testing, but require more corrosion maintenance than chrome-lined barrels. For a competition or precision hunting rifle where every quarter-MOA matters, stainless match is the appropriate choice. For a defensive or duty rifle, chrome-lined chrome-moly is more practical.