RE: 243 for coyotes?
243 is an excellent coyote gun. That is all I really use anymore. I shoot a handload with Hornady 75gr HPs and I've only left an exit hole on a 'yote twice in 2 years of using this load. I do not have it loaded to max, it is around the 3100fps mark (advertised in the book, I've never chrono'ed the load).
Do NOT shoot them in the head if you want to save the pelt. This usually makes a total mess out of 'em. Shoot 'em behind the shoulder like you would any other animal, and try not to hit a shoulder as it will more than likely totally destroy the pelt.