From Madbull, these are fully licensed Daniel Defense style Aluminium outer barrels. Tough, light and high quality; Madbull makes some of the best outer barrels around and they offer them in a broad variety of lengths. A standard M16 has a 20 inch barrel while the standard M4A1 has a 14.5 inch barrel but the beauty of the M16 family is their ability to modify the length with a lot more options then that.
An 12.5 inch barrel is a CQB option as it is 2 inches shorter then the standard carbine length M4A1. It may drop in a little bit of power and accuracy but not by too much and the 12.5 inch barrel combines nicely with 9 or 9.5 inch RAS front kits for a nice, sturdy CQB length carbine.