ORIGINAL: bigpapa
Wait a minute. Knockdown power? Not to be odd about this but your talking about pellets to the neck and brain notto the body of the bird. If you get a #6 pellet in the kill zone then it will do the job just the same as if you get a #4. My feeling is that you want a shot size that will set a pattern to put as many pellets in thespine and brainnot knock the bird down. Use what will make the pattern work.
Okay, maybe knockdown power was a poor choice of words, but a number 4pellet will penetrate better at long range than a number 6 pellet will. Short range, I agree that #6 will do just as good of a job as #4s.