Would this work for our chickens, I doubt they'd sit still like a tame bird would but it should be fairly easy, hold them by their feet upside down, the calm down a little, then head first into the bucket of co2, you could even put a lid with a hole cut in it to kind of stick them in w/o being able to get out so much. They breathe the gas, knock out, and then die. A minute or two later, bird is peacefully / painlessly gone, then we can pluck, behead whatever we need without having to worry about it going wild, shaking blood everywhere etc etc?
Just some thoughts, if this won't work, please tell me, and why if it's a bad idea.
As a way of killing a chicken, it would probably work fine.
But if you want to eat the chicken, you generally want the blood out, and what you suggest would not work as well as some of the other methods people commonly use.