The standard HK93A2 utilized a fixed stock while the HK93A3 used a retractable stock. The HK93 series had a redesigned semi-automatic trigger pack and metal shelf installed in the trigger group well that made it impossible for it to fit a full-auto trigger pack.
The HK93A2 model had a fixed stock, whereas the HK93A3 featured a folding stock. The HK93 series underwent significant redesigns to its semi-automatic trigger mechanism and added a metal shelf in the trigger group well, which precluded use of full-auto triggers.