Bert Popowski would have killed even more crows if he shot 6's or even 7 1/2's. So would you.
I never met Mr Popowski personally, nor saw him shoot crows. I do recall reading some of his articles, probably in the 1950s. He was shooting in the mid-west, don't recall the state for certain now. As i recall his writings he began on the premise that the crow was a large bird & needed large shot. Some birds either escaped or required extra shots which he felt should have been killed with the first shot. This led him to experiment & he even plucked some crows & realized the were not near as large minus the fluffy feathers as they appeared. He then progressed to smaller shot.
Now I have only his word for this "BUT" He hoimseld stated that his kill ratio went "UP" when he switched from large shot to smaller shot. Who am I to say he was wrong???
#9 shot will kill a lot more effectively than many give it credit for, I personally don't like using it on any "Game" which I intend to eat. I have eaten a good bit of "Crow" in my life but not intentionally & it wasn't the type which wears black feathers.