Remember that a fast rate of cooling is nearly as important as the temperature. You want to freeze the alloy in an amorphous state.
As far as rifle cartridge brass goes, this runs counter to what I've read in a couple of different places, from people who know their stuff including JB and the instructional video below from Anneal-Rite:
https://www.youtube.com/watch?v=EXLPGcSNyUs
