Buy a tempilstik rated for 475 degrees Fahrenheit. Maybe $20. Apply to inside of case necks. Stand brass in a pan and add water until the water level is just below the shoulder. Heat case with blow torch until tempilstik paint melts then tip brass into water. Cheapest fastest way to temper.
perhaps you mean 750ºF
475ºC (880ºF) would be too much
475ºF would not anneal (it takes 1 hour at 600ºF)