This is all very interesting and quite viable if one is into doing it but doesn't have much to do with the original poster's question and intent. The 308 (and most of the calibers mentioned) will kill a muley at reasonable distances, with reasonable bullets and good bullet placement. Asked and answered.
Granted and I did not segue into it very well. I merely offered my military training as an example of WHY NOT to do something, IE, dial for wind, and also to maybe help the un-initiated understand that wind calls get progressively more difficult, and affect the trajectory more, as the distance to the target increases. I'm in full agreement with Bushcraft that a 400yd shot on game is both ethical and doable with hunting gear without having to quit your job to learn how to do it. We just differ on a few of the particulars. Some preparation, knowledge and range time is essential, but stretching from a 250 yd capability to 400yd is much less problematic than going from 400yd to "way out past Ft. Mudge".
If you aren't willing to devote the time to it then Scot's approach is best, but I think a 50/200 zero, then just memorizing the fact that the 300yd drop will be about 6-7in is superior to any max-point-blank shenanigen even if you make 300yd your cut off.