Update: there’s at least one report of 40 caliber bullets being used.
A spokesman for the St. Louis Police Officers Association, Jeff Roorda, says that “it appears” the police officers were shot with 40 caliber bullets.
http://www.msnbc.com/morning-joe/watch/police-spokesman-discusses-dead-cops-remark-412716611767
okay, so I’m going to display my ignorance. what rifles shoot .40 caliber bullets?