For a backpacking grouse gun, consider a either stock Ruger Mark IV 22/45 or adding some aftermarket love to one. The old SS Mark II target filled many horse-camp pots of arroz con pollo de trueno....

Pro Tip: Head and neck shots only boys. Have heard too many stories of watching a ruff or big blue fold after making it well out over a steep canyon before succumbing to being perforated. Don't feed the 'yotes....