Each range is gonna have its own set of rules. The one I go to stresses no rapid fire (double-taps are OK), and no sandals.
For your range, their reasoning is probably: shorts and sandals don't provide enough protection from burns (hot brass between your toes would hurt like hell); aluminum and steel-cased ammo isn't reloadable, and they probably collect and sell the brass (takes too long to sort through aluminum/steel); surplus or foreign ammo...who knows to what specs those are loaded. Brass is suspect. Also, all steel-cased ammo is foreign-made, AFAIK, so it's a double coverage type thing.
"Ask not for a lighter load. Instead, ask for a stronger back."