Best Cartidge for Ultralight Sheep Rifle?

[Bearded Gnome]

6.5 Swede in a fast twist barrel? Only a suggestion. A modern sleek missile of a bullet in a medium weight should knock sheep down. I know, not shiny and new enough I suppose. Not trendy at all. Just a thought from a boomer that thinks a lot of that cartridge.
Look at the Hobbit Rifle and Ultralight Ultralight threads. Perhaps a single shot in 6.5X55 could be the ticket? Be Well Brothers, The Bearded Gnome.