If using heavier than lead you get more pellets on target that out penetrate lead.
Federal heavyweight 7's from my 20 gauge will hit about like a lead #4 but have a much greater pattern.
I shot a bird a couple years ago at 52yd with Hevi13 #7's and had pellets break the near humerus and femur along with cleanly shooting through the brain and spine. The turkeys and coyotes I've shot with HTL 7's have been absolutely smashed.
