You just might have a new choice available...Hornady is introducing the 450/400 3" - .400 Jeffrey cartridge in conjunction with Ruger for their No. 1 rifle...

They will have the loaded cartridges firing a 400 gr bullet at 2,150 fps and 4,000 ft lbs of energy...

I also agree that Hagn is probably one of the best single shot action makers out there...