I empathise with you... although I don't hunt anything anymore (except tin chickens), a well matched .22 rifle & pellet takes some beating.
BisMags in .177 can be a sort-of answer, but for longer ranges their traj' is loopy, they still retain less energy than .22s, and have a habit of blowing all over the place in wind past 45 yards.
Depends on which gun, and your barrel - but I'd be inclined to keep trying with light - medium .177s, or go back to .22...
Just for the .20 zealots - 'they' say .20 JSBs have the best of both... faster than .22 with (slightly) more retained energy. But I don't personally care about that.