A pneumatic "kabuki" style head hit.  Bulky, heavy, but cheap.  It uses a modified sprinkler valve, some clippard pneumatic parts, and off the shelf from home depot parts.  It's basically a potato gun that shoots fake blood and goo.  PVC can be dangerous, if it fails it's very sharp fragments flying around at high speeds.  That's not good.  This is being rebuilt with stronger materials to reduce weight and improve the safety factor.  It works great for big messy sprays..