The .45 ACP for bear beats nothing, but not much more. When you compare the .45 +P, 165 gr. bullet, with a ME of 573 ft/lbs and the lowly 30/30 Winchester, 170 gr. bullet. with a ME of 1827 ft/lbs, you get some idea of what I mean. I lived in Alaska for five year and hunted both Black and Brown (Grizzly and Kodiak) bear every year I was there. I carried a Winchester .338 Mag. Over-gunned for Black Bear, yes, slightly. About right for Ole' Grizz. But under-gunned on Kodiak Island. Second year I switched to a .375 H&H for the island hunt.
Don't mis-understand, I love the .45 1911, but it is best used on two legged varments, not four legged ones, especially bear.