When I was loading the 577/450 Martini Henry, I used turned brass cases shipped to me from England. I'd set the cases mouth up in a pan of ice water about halfway up the side of the case. Using a propane torch in a darkened room, I'd heat the neck to a dull red and then tip it over into the ice water. This made the neck a bit softer so it didn't split. I'd do this about every 3rd time of reloading. Never lost any of those expensive cases to neck splits. I would also only resize the necks just enough to hold the bullets.