As has been said before plenty of old timerd like tom Cole and the Hardy brothers took buff using 303"s.with single shots so do abit of research Duncan ya might be surprised.
This hard living ain't as easy as it used to be!!!
If you can hit a dinner plate at 80 metres you can kill a buff.if it's shot in the right spot.a .243 would probably do it.I would not recommend any of the.22 chamberings even the swift it's not going to get through the skin and into the vital organs
.22 winchester .22hornet .222 .243 7mm rem mag cbc 12g