With a grizzly, a .45 is scarcely sufficient unless the shot is very luckily placed.
There are numerous cases of .357 hits merely angering grizzlies, and a .44 magnum having 3 times the muzzle energy of the .45 ACP is the bare minimum to have in your hand if you want to fend off a grizzly.
Not to mention it’s hard to shoot accurately when you’re shitting your pants.