A easy way is to get a big coffee can and punch a bunch of 1/4" holes in the bottom. Build a charcoal fire about 4" deep wrap the cases in a layer of aluminum foil and cover with more charcoal, and let burn out and cool over night. Pull the aluminum foil package out and your done. For larger amounts of brass a metal bucket can be used. Set it up on a concrete block to help with airflow and to protect where its setting from heat. A blower could be used for more heat but will burn thru the foil and may melt brass if to much