From a
CNN article about the hunt for Christopher Jordan Dorner.
http://i2.cdn.turner.com/cnn/dam/ass...al-gallery.jpg
Caption: "San Diego Harbor Police officers near Naval Base Point Loma armed with high-powered firearms walk along a street on February 7 in San Diego."
When cops use an semi-auto AR, it's a "high-powered firearm." If a civilian has the same gun, it's an assault weapon.