Ok here is the deal. I'm a small town cop looking for a good duty rifle. My city is cheap and I have an 870 right now. My Chief is willing to sell me his AR-15 with extras for $750 but I'm wondering if the .223 is the best round for law enforcment use. Other options I have in mind are some AK variation or a Kel-Tec SU-16. I would like to spend less than $750 though... any suggestion?