How does autofire work?

By default it appears that the guns open fire whenever a target is in range, but at the same time, often during planning stage I would see guns that are fully loaded, pointing at a target - shouldn't this never happen since they should fire the moment they are ready?

Also, how is autofire aim compared to manual aiming? Naturally with manual aim you easily miss since in the delay between round start and gun firing, the enemy ship could have pulled off an unexpected maneuver. Autofire on the other hand, seems to always fire in the general direction of the enemy.