If you select a railgun turret ghost, then pressing the 'R' key rotates it by 45 degrees each time as the railgun turret has 8 possible orientations.
If you copy a turret into the cursor, pressing the 'R' key rotates it by 90 degrees each time, meaning that some orientations are not possible to achieve this way.
It's a minor one, but I came across this by placing a railgun turret and setting the target priorities. I then copied the turret so that it would copy the target priorities, but I found I couldn't then place the turrets facing at 45 degrees to the original.
Workaround is to use a turret ghost and then manually copy the settings using Shift+Right Click, Shift+Left Click.
[2.0.20] Cannot rotate a copied railgun turret in all directions
Re: [2.0.20] Cannot rotate a copied railgun turret in all directions
Thanks for the report, I think this is not a bug. If you copy an entity, it behaves as if you made a blueprint of the entity and blueprints can't be rotated in 8 directions.