When Microtech Small Arms Research (MSAR) started tearing apart the AUG they discovered many engineering shortcomings that were easily resolved by modern technology. After deciding to go ahead and manufacture the STG-556, Microtech invested a few million dollars in procuring many computer-aided CNC machines that could keep very close tolerances with minimal rejection. When they are not used to make rifles, they are easily set up to make knives.
The benefit of their process is seen in the final product. There is no need for gauges to check for headspace or special fitting. Tolerances and quality control are held to such rigorous standards, any STG-556 part will work in another STG-556.
The Steyr AUG was designed as a family of rifles that could be quickly adapted to meet a variety of situations with a quick change of the barrel. The STG-556 maintains this modular design allowing the user to quickly configure a carbine with optional Picatinny rail attachments that is capable of securing the availably array of lasers and optics.