Daniel Defense
Daniel Defense's 12.5" Government profile cold hammer forged 5.56 barrel on carbine gas, sold stripped or with a low-profile gas block or front sight base.

The 12.5" Government profile barrel is the top of Daniel Defense's short-barrel range before the 14.5" mid-length. It is cold hammer forged from 4150 Chrome Moly Vanadium steel, chrome lined, and finished in mil-spec heavy phosphate, the same process the company uses on its complete uppers.
Gas stays carbine length at this size, and the journal is .750" so any standard low-profile gas block fits. Daniel Defense lists three configurations: stripped at 1.40 lbs, with a low-profile gas block at 1.48 lbs, and with a front sight base at 1.71 lbs. The muzzle is 1/2x28 and the extension is A4.
12.5" is the length that gets the most out of 5.56 without going full carbine: it keeps velocity closer to a 14.5" than a 10.3" does, and it takes a 12" to 12.5" rail so a light and a laser both have room. Like every sub-16" barrel, it makes the finished rifle a short-barreled rifle unless it is built as a pistol.
Add the Daniel Defense 12.5" 5.56 Government CHF Barrel to your build and see how it enhances your platform.