The STG-556 is a Steyr AUG A1 a clone manufactured by Microtech Small Arms Research (MSAR). It was introduced at the 2007 SHOT Show. The STG-556's working system features a bolt release as seen on the M16 rifle; otherwise, the STG-556 retains the features similar to the Steyr AUG, such as having the quick-change barrel option and the ability to change which side the weapon ejects from by changing the bolt out for a right or left side bolt respectively.