There is Player 1 and Player 2.
Player 1 enters /gun Player 2 - if Player 1 and 2 have Full Trust, it will work.
Player 1 is changed into a playertype resembling the default Gun, whereas left-clicking will fire the gun (Player 1).
Player 1 is mounted to Player 2's hand.
I'm guessing the OP wants this to add a twist to cooperative gunplay? Where Player 2 aims, and Player 1 is the gun with a mind of it's own and fires when it needs to.