Amnoxx

Hello, I've always used space bar for firing in World Of Tanks and id like to be able to bind that to fire all guns that is defaulted (And not rebindable?) to double left mouse button. However this doesn't seem to be possible as i firstly cant find the binding for "fire all guns" or for that matter binding a keyboard keys to any of the existing ones, i get the message "You should use mouse keys for this command" when binding to fire.