"The gun-nerd site Forgotten Weapons has offered up a glimpse of the bane of 19th Century elephant hunters: the dreaded 4-bore. It chucks a one-inch quarter-pound ball (1,750 grains). Frederick Courteney Selous used a 4-bore muzzleloader in the 1870s. It got the job done, but Selous complained that the brutal recoil upset his nerve. It’s certainly a flinch-inducer."From recall, he killed a lot of elephants with a four bore...then accidentally double loaded a barrel. He developed a flinch he could never quite get rid of.
My son in Alaska was urged to carry a big bore revolver with recoil so heavy you couldn't control it and still not enough thump to stop a black bear let alone a Brown or Grizzly. I got him to carry a Glock 19, with 15 9mm penetrating rounds. Controlled firepower baby....15 rounds in 1.5 seconds has to be better. Maybe you'll luck out and hit a vital. A guy in Alaska makes a 147 grain 9mm penetrating round for such an event.
https://www.wideopenspaces.com/alaska-man-kills-charging-brown-bear-with-a-9mm-pistol/