Currently, there's a set time for when the Turret kicks back in. The issue is, eventually, the raider will understand how long that delay is and take advantage of the gap in shooting.

I propose that the delay in shooting be a range as opposed to a set time. For instance, instead of setting a delay of 15 seconds, set a range of time between 3 and 20 seconds and make it so that it could be 4 seconds, 12 seconds, 5 seconds or 15. 

This would make it much more difficult to know when the Turret will start shooting again and it will make it harder for raiders to approach.