I'm looking to add an AR to the collection. I want it for the fun factor (shooting once a month or more), but also as a great, reliable combat gun (both for home, and you know, zombies). I would really like to keep it under a grand. The lower the better. There are a lot of AR's on the local classifieds, but I don't know anything about them. Caliber choice? Wanna kill these ads? We can help!