Field reference · AR-15 & AR-10

AR Caliber Guide

Popular AR-15 and AR-10 calibers: what each is good for, a typical load and barrel, speed, energy, practical range, and which parts you have to change from a standard rifle. Tap a column header to sort.

	Made for	Typical load			Practical range		Twist

Reading the swap column

Each caliber lists what you'd change starting from a standard 5.56 AR-15 or a standard .308 AR-10. "Keep" means the standard part works. Calibers that keep the bolt and magazine can usually swap with just a complete upper or barrel. Always check your bolt and magazine with the maker of the upper you buy; some rounds feed best from purpose-built mags.

AR-15 vs AR-10

The AR-15 is built around the 5.56 case (about 2.26" overall). The AR-10 is a larger receiver built around the .308 (about 2.80"), so any round on the .308 case family drops in with just a barrel. Parts between AR-10 brands (DPMS and Armalite patterns) don't always interchange.

Keep in mind

Never mix .300 Blackout and 5.56 ammo; a .300 round fired in a 5.56 barrel can destroy the rifle.
Velocities are typical factory figures from the listed barrel length, from my own knowledge, not looked up.
Practical range assumes a good optic and the right bullet for the job.