Actually, thats not true, now the police carry a shotgun, .40 USP, and an AR-15, in CA at least
I dont know about that, a bullet from an M-16 is much more lethal then a regular higher caliber rifle round. The small round enters the body and become round, jagged and ricochets off of bones (because of its low mass), slicing through organs, tissues ect. and will cause much more damage then a normal bullet.