was going to make a new thread on this but hell I will just add it here.
Top Tech is a subsidiary of G&G. this is not GBB and not a conversion. it is still an AEG, see toptech101's other videos for more info. other videos show how it works. Kind of a neat idea but weak and lame at the same time.
a 3D Animation to explain Top Tech Blow Back
YouTube - Blow Back Axiom