Thank you! I appreciate it; that's quite helpful.I've never done manual dislocation. I've always been worried that I didn't have the strength in my hands and 6 month cockerels are pretty tough. I don't always feel the stretch the first time which is why I now do a double pull just to be sure and you can definitely feel the elastic stretch on the second pull.... I think the first pull I'm just too keen to give a good hard quick tug rather than "feeling" for it. There is barely half a second between 1st and 2nd pulls, so they are not really two distinct efforts.
You could probably also use roofing felt to make a cone.... anything that has a bit of rigidity to it perhaps even cardboard. I use Duct tape to secure it in the cone shape and screw it to a piece of plywood that I can hang up. I much prefer to be able to drop them into the cone once I've dislocated, then cut off their head and walk away and take a few deep breaths and chill before I return to deal with the carcass. The killing is by far the hardest part for me, so having that walk away period to compose myself whilst it spasms makes it a little easier.