I like to think that even though the MCH is a physical job, and I think this for every job, they use magic. Now not a lot of magic like casters and healers but but some magic. I mean this already kinda makes sense since the MCH's bullets are made of aether with the use of the aethertranformer on are waist. I just assume that it also allows us to materialize or manipulate technology too. The bioblaster, drill cannon and auto-crossbow are just are gun being rearranged into those other weapons. Maybe the aethertransformer is also a pack were we keep spare parts and when we summon rook we manipulate those parts into it and same with queen.