Use a 12g with open choke (cylinder/skeet) and light shot (3 dram 1 1/8 load in 6 or 7.5). Aim high. I don't really like 22lr for grouse cause I don't shoot at them on the wing with a 22 and its hard to make a head/neck shot when they are on the ground running. If you hit them anywhere else with a 22, chances are that they are going to keep running and you may or may not find them.