Forget the name.
The gun DOES NOT use APS system (made by Maruzen)
OR VSR system (made by Tokyo)
It uses the new TM L96 AWS system (based on VSR10, but shorter piston and cylinder).
PDI makes the zero trigger kit... not sure about anyone else.
http://www.x-fire.org/etop/tm_l96.html
Also, that pin looks to be the lock for the safety lever or bolt rotation.