Heckler & Koch MPK-11

Heckler & Koch MPK-11 is submachine gun. Possibly the most used Solo's gun in existence, the MPK-11 can be modified into three different designs, including a bullpup configuration, standard SMG, an assault carbine, and it will accept a grenade launcher mount.

Source

 * Cyberpunk 2020, pg.61,62,63
 * Blackhand's Street Weapons, pg.20