After normal Skeet ranges, the birds aren't very dead with 9's
Up close, all shot to hell.
My breaks are never as strong with 9 's as 7.5's
I routinely shoot low gun 410 skeet with a full choked gun. Avg this mos is 22. Not world class, but I'm seeing a couple hundred breaks a week preparing for an upcoming tourney.
I describe #9 breaks as "erosive" whereas 7.5's as "crushing"
So, in my view, for killing, a 7.5 does a better job, but for scoring at skeet ranges, there are away more 9's in the pattern.
