When building a light weight AR, you want reliable function, you want high quality, long-lasting parts, and you definitely want a barrel that is tough and made to tight tolerances. The ODIN Works 16.1 416R Stainless Steel ULTRAlite Barrel comes standard with a .223 Wylde chamber so both .223 and 5.56 NATO ammo can feed, fire, extract, and eject without a problem.