Dead Air Suppressors ship with a 7.62 cap. Get this to adapt your world-class suppressor for 5.56mm barrel. Dead Air makes a cap for 7.62, which will work for all calibers on the Sandman and Nomad, or you can improve the sound reduction by just a smidge (that is a technical term) by having a 5.56mm or a 6.5mm for those specific calibers. You limit the flow of gas out the end of the suppressor, thereby allowing for a small reduction in sound.
This cap is for 5.56mm / .223 caliber firearms.