Hello Dave T.
Like cheap tank stated,if the rubber seal is not in it's proper place the gun will not shoot right ( or at all ).I struggled with one or two of them until I finally got it installed right. Been to long for me to be of much help in giving directions on how to do it right,but there are others here who can give you the right info on how to fix it.It is a simple fix if you know how to get it in and get it in- in the right spot and direction.

BIGMIG

P.S. you do not need to tear the gun shooting mechanism apart to fix this.............