SAJewersNot sure if this is true, but according to this post on SPUF, the Short Circuit now only uses up metal when it destroys a projectile: http://forums.steampowered.com/forums/showthread.php?t=3216739
That's what it means "per projectile destroyed"
As Twilit said, the firing rate is the real problem. 8 stickies only "cost" 120 metal, mean you can put down a minisentry and still negate a large portion of a demo's damage.