I use a drill, an extension, a socket, and a propane torch. Find a socket that fits the base of your case, insert the base into the socket, with the drill rotate the socket slowly over the propane flame and look for the color change at the neck/shoulder. Be careful - its not hard to overcook one. Drop it into a pan of water when the neck shoulder area start to turn color - not red, but you'll see it change color and reach a 'purple' - go no more.
I too tried to hold the brass case and didn't think I was getting it hot enough to do any good. The torch/socket method enables you to heat the case a little bit longer without getting burnt.
