nevermind have sorted it
it anybody else was looking for the same thing but wasnt sure how here is how I did it...
1: created a 50% transparent sprite
2: added an even when I click ont he turret to move the transparent sprite to the turrents X & Y location
3: set the transparents sprite width and height to the range of the turret
This creates a 'view type' effect around the turret and shows you how far the turret can see on the map.
Might not be of interest but just in case thought I would share.