Tried the CB long on gophers yesterday.
I had problems with the distance in the beginning. I had my scope and everything set up for 75+ meters.... but the buggers kept popping up around 10 and 15.... so I had a couple of misses.
the hits were positive. the thud was very distinct when the gopher was hit, but the reaction was that of a wounded animal. Head hits were the exception, but I never had a body hit that stayed put.
I switched to Winchester Expert, that have a generous HP and are a lot cheaper than yellow jackets. Biiiig difference!!! Like Yoyo said, even with a good HP, I doubt that CBs would give visible results.
Sure, the gophers die, but I don't like to cause undue suffering to any animal. I doubt I'll be using them anymore, except for the situation where noise is an important factor.
I have no idea how would they work on grouse, but there is already a lot of debate regarding the ethics of using rifles, nevermind the use of underpowered ones.