I just made this cannon the other day. its much more compact from the rest of the cannons. There are three major improvements. It has a removable barrel that is an inch in diameter, an electric valve with an electric switch, and it has a pressure gage to get a more accurate pressure reading. parts list one electric sprinkler valve 1" 8-10' of 1 " PVC 2-6' of 1 1/2 " PVC two 1" three way PVC parts that are threaded in center joint two 1" male threaded connecter two 1 1/2 " end caps one 1" end cap 9 volt snap one 1 1/2" X 1" X 1 1/2" three way trigger/ switch pics http://www.makezine.com/blog/archive/2006/06/henrys_air_cannons.html