A friend helped me with the broomstick method and it was amazingly calm and effective. We used feed sacks, cut off the corner, hold the cockerel upside down until they calm, lower them into the bag, head out of the corner, lay them down chin first on the ground, broomstick over the neck just behind the head, feet gently on broom either side of head, raise their legs until you feel the click of dislocation.
The placing of the broom is vital because it needs to be just behind the head - not too high, not too low. Also key not to put too much pressure on the broom - you're not crushing or breaking the neck but dislocating it.
Because it is technical, it's best to get somebody to show you/do it with you. I did the last one by myself but would still not feel confident to do it entirely alone. It was also helpful to have somebody else around to help with the plucking and to show me how to dress the bird (but that bit I would be OK to do on my own next time).
I'd certainly rather do it this way than anything involving a gun but that's because I've no gun experience.