Hevi shot is no hype, and you do need a choke tube rated for it. What kind of tube do you have? I've never shot hevi shot out of my 870 but my 835 loves 3.5" 2.25 oz #6 hevi-13s. My state doesn't allow shot sizes smaller than #6, I tried to enlighten the DEM last year when they were modifying regs, but they just didn't get it.