Update since my last post:
My new favorite "pin gun" is a S&W 610, 6 1/2" loaded with 180 gr. Montana Gold flat-points and max load of Longshot. This load crono's about 1350 FPS out of my gun. This load drives 'em off the table with authority. The heavy gun minimizes muzzle jump and the moon clips speed reloads. I've done better with this than anything else I've shot.
We have found that in cold weather, the pins will shatter quickly. For the winter months, we set up the club's plate racks with bowling pin shaped plates (official size and lazer cut). Not the same but it keeps you in practice and lighter loads work well.