M4A1-S is one of the most popular weapons in CS:GO. The main advantage of the M4A1-S is its ability to attach a silencer to it, which provides soundproofing and reduces recoil. It has been painted using a picture of the original gun as a template. Exchange your Soul Gems for the M4A1-S Master Piece. The M4A1-S Master Piece is a variation of the standard assault rifle M4A1. It is one of the few weapons that has an exclusive finish called Master Piece. The name of this weapon comes from the fact that it was painted with a very expensive gunsmithing technique called "Master Piece". Exchange your Soul Gems for this weapon!