2 issues intertwined
Remotely firing newly loaded turrets does not fire them, they still track your mouse cursor though.
As soon as the turrets received a target to shoot at, with either 'selected target' or 'any' with pirates nearby, then you can fire the turrets remotely as well.
However, the projectiles will not go to your mouse cursor, but instead to the last position of the target it was set to before you took control with the rail turret axis.
# So if the turret has no target, remote firing won't fire the turret.
# If the turret had a target assigned in the past and you try to remote fire, it will fire but not at what you're looking at, but at the position the previous target was at.