You probably have a good idea about dumping htem into water to prevent over annealing or at least getting hot brass out of the work area, but brass isn't a very good heat conductor. Once you get your neck/shoulder annealed, the annealed portion isn't going to spread after removing the heat- the brass needs to be heated to a certain threshold before it anneals, the heat migrating through to the cooler brass will bring the temp well below that threshold.