First revealed at the 2007 SHOT Show, the STG-556 was manufactured by a subsidiary of Microtech Knives, Microtech Small Arms Research. Little is known about the history of the weapon other than that.
Despite being regarded as a Steyr AUG A1 clone, the STG-556 is not truly a clone of the AUG due to some differences. One notable difference is that the STG-556 has the bolt release mechanism from an AR-15 located on the left side of the rifle. Another difference with older versions of the STG-556 is that its magazines are not STANAG-compliant; instead, it uses proprietary clear-sided magazines that resemble the ones used by the AUG. However, later versions of the STG-556 are able to accept STANAG magazines.
- STG-556 Limited Edition
Limited edition run of the STG-556; this version is very much like the standard STG-556, except that it uses a Steyr AUG A3 body. 1000 weapons were made, all finished in black. 232 more were made with a 18.5 in (47 cm) barrel after it was discovered that the 18 inch barrel had better barrel harmonics than the standard full-length 24 in (61 cm) barrel.
- STG-556 Gebirgsjäger
Limited edition run of the STG-556; this version is the exact same as the STG-556 Limited Edition except that all weapons had a drab green finish. 500 weapons were built.