I don't know if It's crack your smoking or what, but I wouldn't use an air rifle for a bird of that size.

Sure there's a chance that you could kill it with a properly placed shot with a good airgun, but what are the odds of that? Most of the grouse you will encounter that will have been hunted before and are a little skittish. Meaning they won't sit there and look at you while you put a bead on it's head.

If you go father into the woods you may find some that have'nt been messed with and maybe get them when they fly up in a tree and look at you, but I wouldn't count on it.

Get a .22 or better yet a shotgun. You can go get a cheap single shot .410 at Wal-Mart or something and it probably costs less than the air rifle in question.

Good luck happy grouse hunting. I think I'll go tomorrow on the way home from fishing.