I wish to congratulate every one concerned with wanting to make head shots on grouse with a 22. I was 12 years old when I started bringing in grouse shot with a 22 and I got hell, if a grouse was shot in the body.
I later taught my boys, then grand sons to do this. None of them will shoot a grouse in the body with a 22, unless there is special circumstances, nor will they (any of us) shoot a grouse on the ground with a shotgun.
We say head shot, but actually it is the neck that is usually hit. Aiming at the neck allows for small errors of range.
I can see yu wanting to get a new rifle, but there are so many good used 22 bolt actions out there. My grouse gun for 50 years has been a Winchester Model 69 with a good Lyman aperature, close to the eye. What ever you get, it must have a good trigger and either aperature sights or a good 22 scope. I prefer good aperatures, especially for off hand shooting, which is often the case with grouse.