RE: BLR Caliber
Yes it is relative but......
The more powder a cartridge holds the longer the barrel needs to be to burn all of that slow burning powder.
Magnum cartridges loose more velocity per inch of barrel than does a standard cartridge like a .270 which looses more velocity per inch of barrel than does a short action standard cartridge like the .308.
Like I said you will still have greater velocity with the WSM but not what you would expect if you go by the published data.
BTW this is not meant to talk you out of any cartridge but rather to give you something to think about concerning your decision. Honestly in the BLR you would be better off with the standard magnums that you would be with the WSM's.