The button to change seats in a vehicle is C and i'm pretty sure the button to remove a stationary machine gun is whatever you have melee as.

well i put my melee as C so when i'm in the back of a truck firing the gun and i push C to get into the drivers seat...it puts me in the seat but the machine gun dissappears too.

When i exit the vehicle i get bugged and cannot move my character or move my mouse. I can only fire and zoom.

obviously its easy to avoid but just thought i'd throw it out there

thanks.