ORIGINAL: North Texan
The .223 will kill coyotes as far as you care to shoot them, as will the .222, .22-250, and .220 Swift. The .223 just has a lot more choices in ammo. Of course, Black Hills is all you'll ever need.
Exactly my thoughts, many squad snipers in the Marines in Iraq are using m-16's w/ scopes, and are getting kills outwards of 500-600 yrds. My uncle was telling me about it when he came back, and I read an article about it in American Rifleman. The 223 plenty of lead.