AR-15 Barrel Length: What Actually Matters

Velocity is a tax, not a feature

Every inch of barrel is somewhere between 20–35 fps of velocity on a 5.56. That adds up fast at longer ranges — a 10.5" loses real terminal energy inside 150 yards.

The sweet spot depends on the role

A 14.5" pinned carbine is the honest best-of-both. A 16" is more forgiving to host setups. An 18" DMR stretches 5.56 or opens up 6mm ARC.