KAC Free Float Rifle RAS (MK12 Mod 1)

The Knight's Armament Free Float Rifle RAS is the quad rail that turned the MK12 Mod 0 into the Mod 1. As the SPR matured, units wanted standardized Picatinny real estate on all four sides for lights, lasers, and the bipod that designated-marksman work demands, and the round PRI carbon tube could not provide it. KAC's rifle-length free-float RAS (P/N 21318) was the answer and became the defining feature of the Mod 1.

Full-length MIL-STD-1913 rails sit at 12, 3, 6, and 9 o'clock, and the rail free-floats the 18-inch stainless barrel for the harmonics an SPR is built around. It ships with three KAC 11-rib panels to cover the unused rails for a comfortable hold. Installation uses a KAC proprietary barrel nut over a low-profile gas block.

This is the Mod 1 tell. A Daniel Defense or M-LOK rail on an 18-inch barrel is an SPR-style rifle; the KAC rifle RAS is what makes a Mod 1 a Mod 1.