It's a drop-in replacement for a mil spec buffer and buffer spring and it's designed to eliminate the noise from the regular buffer spring - see the video.
This one is the Carbine (3.3oz) weighted version - it's recommended by Armaspec to replace the H Buffer but you can get heavier weights from Armaspec - again, see the video.
It will work with a mil spec AR15 lower, BCG and buffer tube in .223/ 5.56 and .300 BLK.......NOT .308.