I have a fresh refurb Diana 460 that seems to have an issue.Power level drops from 21 for with light wadcutters to 18/19 with JSB 15.9's, and then to 14 with 21 grain Baracudas. It also has some light spring rubbing during the cocking stroke.I'm wondering if this could indicate a broken spring, or just a tired one.Thoughts?Thanks all!