We have been procuring AR's for several years now. Patrol officers have had the option of carrying their own rifle for 25+ years. Minimum caliber .223, max .30-06, no magnums allowed, scoped or iron sighted. 30 hour intensive course and anual qualifications required. I carry two, a Colt AR-15 Gov't Carbine and an HK-91. Depends on the situation which one I go to.
Goal is to eventually have an AR and a shotgun in every car. The presence of a rifle (especially an AR) in a volitile situation tends to scare the bejesus out of the run of the mill turd. They assume SWAT is already there. I have had several armed subjects drop their own long guns and give up or run away upon seeing the profile of what looks to them to be a machine gun.