Love the 45-70. I have the marlin guide gun. Anyway, depends on the bear and the shooter as to the "best" gun for the job. Big black bear (300 lbs +) = .270, .308 range. In revolvers, .44 mag and up isn't to bad on decent blackies either. .444 marlin and 45-70 are awesome thumpers.
For real bears, I mean brown bears, you need to kick it up a notch. Think 30'06 as your bare minimum starting point and work up from there. Basically you want to shoot the biggest gun that you can shoot accurately. The various 300 mags out there are great with tough bullets such as nosler's for most applications. .338's are even better. Forest service carries .375's but most can't handle that sort of cannon. 45-70 loaded hot is good as well (carried that guiding). Old school can go 35 whelen.
In terms of moving after shot... most do, even if the first shot was a killing shot. I've had double long shot brownies run over 50 yards before. Best to keep shooting until the beast stops moving.
For real bears, I mean brown bears, you need to kick it up a notch. Think 30'06 as your bare minimum starting point and work up from there. Basically you want to shoot the biggest gun that you can shoot accurately. The various 300 mags out there are great with tough bullets such as nosler's for most applications. .338's are even better. Forest service carries .375's but most can't handle that sort of cannon. 45-70 loaded hot is good as well (carried that guiding). Old school can go 35 whelen.
In terms of moving after shot... most do, even if the first shot was a killing shot. I've had double long shot brownies run over 50 yards before. Best to keep shooting until the beast stops moving.