Are AR-15s even assault rifles? I think not, they are a derivative to be sure, but not full auto.
I guess the cops may have installed an automatic sear.
No. They are not.
The AR-15 is a semi-automatic, .223 caliber rifles; very much the same as the semi-automatic, .223 caliber rifles used by small game hunters all over the country. In fact, some people hunt small game with AR-15s.
On a side note, in Virginia it is illegal to hunt deer with an AR-15, or any weapon of a claiber smaller than 0.23. The Commonwealth has determined that anything as small as .223 is not powerful enough to allow for consistent, clean, humane, one-shot kills of animals the size of a deer.