Quite some time ago, I researched, and a vet had posted the 2 most humane methods of dispatching a chicken was either cervical dislocation, or swiftly cutting it's head off.
When they removed my breasts, they also cut out my lymph nodes. This has severely limited the use of my arms, and the strength I have in my arms. It's not like I can ensure I'll have the strength to do a swift, efficient cervical dislocation. I don't want my birds to suffer, due to a lack on my part. I decided I'd probably be best with a hatchet, BUT this too proved to be difficult for me. I didn't have quite enough oomph. Instead, I lay them on a board, the board has a couple holes drilled, so I can loop a piece of twine at the neck, and foot end of the bird. I secure the bird without it being too tight. I then place the hatchet lightly on the neck of the bird, and hit the hatchet with a small 5 pound sledge hammer.
The small sledge hammer ensures I hit with enough force, that it's all done in one fell swoop. The hard part is over almost instantly. Their head is removed. Yes, there is still body movement for a bit due to nerve, and muscle reaction, but I know they are not still alive, and suffering.