Directly from quarterbore
The RAS system clamps to the handguard cap via a clip on the top half while the rear is attached by a clamping mechanism that fits over the M-16 gas tube and fits into a recess in the M-16’s barrel nut. This rear clamp is then tightened via a hex-head screw producing a very tight fit that prevents most movement as experienced in RIS units.
The KAC RAS is NOT free floating , it clamps onto the gasblock ring and the barrel nut whereas the RIS only clamps onto the gasblock ring.
The KAC Free float RAS , free floats. Meaning that it attaches to the barrel nut and which holds the barrel in place but touches no other part of the barrel , increasing the stability of the barrel when more accessories are added to the rails.