I help a couple of dairy farmers with birds eating and pooping on their feed. The barn is the typical post and beam with a metal roof and I have limited myself to super careful shots with a solid wood back stop or only select outside targets. There are some shots I would have liked to take but didn't because of the possibility of ventilating a metal roof. I have a WC II and Veteran Shorty in .25 and a chrony. Could somebody please advise how I might set those up so they won't be metal roof ventilators? Suggestions about reg pressure, hammer spring tension, type and weight of pellet, etc.? Thanks for any guidance.