A .223 will last I bet 3000 rounds. I have yet to burn one out before trading or selling. I love .223. I think its a perfect balance of a varmit caliber. The 220swift too much, 22hornet too little.

A .243 about the same. Dominating factor I bet would be more damage from cleaning. Its hard not to do. Never burned a barrel out yet.

6.5X284. They are really not that fast. Never had one, but know alot that do. I will find out.

Only thing I have burned out is a 300RUM. And due to lack of knowledge how to take care of a barrel, I ruined my 270win, I had since I was 12. I still hunt it however.