Ever considered doing a custom rig on one of the Lazzeroni cartridges www.lazzeroni.com?
Take a look at the ballistics for the 7.21 Firebird (284), the 7.82 Warbird (308), and the 8.59 Titan (338).
For instance, their 8.59 Titan holds ~10grs more water than the 338 Lapua.
Give them a look.
Brass and dies are more than what one is use to, but the cartridges flatout perform.
Dies are from Lazzeroni - $115.00 (just like custom dies)
If you have an existing barrel that can take the reaming of a Lazzeroni, you can rent a reamer & go/no-go gauges for 2 weeks for $45 from www.reamerrentals.com.
Lazz brass can be bought from Lazzeroni or Midway for about $2/case.