If you are not an excellent shot with a .22 forget head shots altogether, because you'll miss way more than you hit. My friends are relatively happy using a .22 and going for center body shots after giving up on head shots. They claim there usually is negligibly meat loss and far less missing.
Now this is all in northern Alberta where you can be attempting 30-40 yard shots. I'm a pretty good shot and have missed more head shots on grouse than i care to admit. Next time I'll try the body shot method for myself. I've had very good luck with a tightly choke 12 gauge and assuming just over the head at up to 20 yards. But one shot with a shotgun often scares away any other birds.
Just to add prospective to this discussion, i recently spoke to a well known gun shop owner in Edmonton and he loves using a browning tbolt in 17 hmr for grouse because of the excellet range, accuacy and rapid fire capability with a relatively light package.
Finally i want to point out that being a good shot with a .22 and being “accurate” with a shotgun even with a tight choke is a much lower level of difficulty.