The C-Tech GP-90 is a modular handgun only used by humans. It is modular in that one can change caliber, magazine configuration, optics, and many other features.
It is specifically designed for a human hand, with three positive contact points. If all three points are not in contact with a hand, the gun will not fire.
Col. Cartwright II carries one configured initially for 10mm caseless rounds with a holographic sight and locked to semi-automatic fire.