I always skin Pheasants and Pluck Grouse ,I also skin Woodcock for what this information is worth ! I have used #10 Shot in a 28 Gauge for years , it is for whatever reason a wonderful Woodcock load and seems to do well on Grouse also ! Like Dave T ,I really never thought shot penetration was a huge deal in Grouse or Woodcock as it surely is in Pheasant Hunting where I have even gone as large as #5 in late season birds that have had a lot of hunting pressure , Well Dave maybe it is just a Pennsylvania way of reasoning !
