It's also why you don't tend to see Armored Core and Mechwarrior meshing. The former imparts flight capability and very rapid unrealistic movement to massive machines via the use of thrusters. If you suspend the disbelief that such a thing would work- then it flows well in it's own right- but you wouldn't put a big, clunky, heavy mech in the same universe that more closely follows physics. 

Something close to what I imagine the GM is going for would be Chromehounds if you aren't going to pick Mechwarrior. Just without the combas towers and loss of mainstream radio communication. Much like Valor said, it's less about a humanoid machine holding a gun and much more a war-machine designed for combat with fixed or turret mounted weaponry. Very few designs in Mechwarrior actually have hands. (which is one of the main reasons I prefer it as an IP to other Mecha genres)


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The big difference with this is that the 'mechs in this are MUCH smaller than Mechwarrior or Chromehounds. About half the size of the smallest mech in Mechwarrior, if my math is on par.