45/70 which you don't want, so I say 450 Marlin. Personally I use a 30/30, ..out of respect, after shooting bears, elk or moose with my 30/30 I always whisper into the dead animals ear, so his soul may be at peace.."sleep now, you were shot with a uber magnum"... it allows them a little dignity.
I also try to keep the gun out of sight as well,.. there is nothing more depressing for a bear than seeing a 336 Marlin, seconds before he tumbles..