I'm considering have my Marlin 1895 45-70 converted to 50 Alaskan - primarily for bears and wild hog. Can one truly expect significantly better performance with the 50, or is 45-70 with high performance ammo entirely adequate?
Buddy of mine used his custom Marlin in 50 Alaskan to kill a cow elephant this summer.......you can read about it here:
lever gun elephant
The conversion has been done successfully by Wild West and Gary Reeder over the years. It just bothers me that you have to open the receiver for the longer cartridge. Myself, I'd rather use an '86 to do the conversion. The cartridge is great, and with the really good bullets out there now, there's no reason you couldn't go after griz and browns.
.45-70 is more than sufficient with the right loads if you are willing to keep shots to 100 yards or less, which you should do in most cases any way with brown bears.