DI water is dirt cheap. Why introduce an uncertainity to a chemical/industrial process ? Heating the brass does open it to all sorts of chemical invasions that can change its characteristics, IMO. Also another good reason to approach shooting brass barreled antiques/repros with a good deal of trepiditation, too !
Not being a metallurgist, can't offer any concrete evidence/suggestions ! As a hairy-knuckled service rep of some experience I can relate I've observed enough incidents of heat/contaminents/alloys to err on the side of caution. >MW