In "Handloading for Hunters", Zutz actually debunked both the large and small shot "schools" of thought. He used #6 for grouse because he couldn't obtain #7 in the early 1970s, when this book was written, and he deemed #7.5 too small to kill cleanly. It was his opinion that #7, if it again became available, would become a "modern classic" for grouse, for the open bbl on pheasant in 1.25 oz loads, et. al. He actually seemed a little peeved off at the "small shot school" for pushing #7.5 so hard that #7 was driven off the market.
I don't hunt grouse or rail, so I'm just repeating what I've read.
