Just curious thinking about rebarreling a rifle for "Groundhog" shoots and was thinking of this. Also looking for something brass would be avaliable ( if needed quick) at the local shops.
There is no reason a 260 won't do well at 600. Plenty of great bullets available. Any 243 brass can be run through a 260 die, opened up, and should work fine. Go with either an 8.5 or 9 twist and you have up to 140 grain bullets covered.