So the Dev said he wanted it to not run on ammunition but have a cooldown. The other stat thread seemed to be wandering a bit so I've tried to start it again. My idea below hopefully caters to the imagination of the dev. I would be very happy if you guys would read this and respond to it!
-Greytower



Level 1: (Compared to default lvl 1 turret)
+15% firing speed
-20% range

Does not require ammunition, but overheats if it fires too much without being hit with a wrench.
Costs 150 metal

Level 2: (compared to default lvl 2 turret)
-25% firing speed
+25% damage

Does not require ammunition, but overheats if it fires too much without being hit with a wrench.
Costs 250 metal to upgrade

Level 3: (Compared to default lvl 3 turret)
+20% missile range
-15% missile damage
-15% missile speed
-15% bullet range
+20% bullet firing speed

Does not require ammunition, but overheats if it fires too much without being hit with a wrench.
Costs 250 metal to upgrade

Missile travels %15 slower but ignites enemies caught in the explosion. (Similar to Cow Mangler 2000) Can normally only fire missile every 10 seconds. Hitting the sentry with a wrench reduces the cooldown to a maximum of 5 but costs metal.

PLEASE LOOK AT MY IDEA AS I FEEL IT IS THE MOST IN DEPTH IDEA HERE!
THANKS!
:D