I buy a lot of practice ammo from Georgia Arms where they buy back the brass.
The other day I was talking to one of the employees about where they get most of their brass and he said law enforcement. He also added he could use all the .45 ACP he could get as there is a great demand.
This leads me to believe that LEOs don't shoot a lot of .45 but the general public does. Anyone know the relative popularity of different major calibers?