I already did the 45 Colt in a 1873 Winchester on a 300+ pound black bear. Mine was an original relined to 45 Colt, 20" barrel, 225 grain SWC cast bullets at about 1000 fps MV.
I did not intend to hunt bear and was invited, all I had was this project 1873 short rifle and the ammo mentioned. The day before I'd sighted it in and new exactly where it was hitting from close up to 50 yards. This bear had killed 3 calves and was chasing livestock including horses, so a predator permit was issued. After a week of tracking and chasing him we took a day off. I rode that day anyhow and crossed fresh bear tracks in wet sand a mile south of my house. The hinds were 9" long X 4.5" wide. The fronts were 5" wide. Next day we met with hounds and horses and went to the spot just south of town. The dogs took off before we hit it and up the mountain they went. My horse was wore out so I decided to travel down the creek and meet up later. Well I heard the dogs and rode to them. I dismounted and walked to one of two dogs that were barking at the ground. I failed to look up a few yards ahead. The bear was waiting for me in a tree about 6 feet up, head downwards and a front leg ready to swat me.
I retreived my rifle from the scabbard and kept a deadfall tree between me and the bear. At about 50 feet I put a bullet into the base of his neck angling into the vitals. The bear disregarded that and turned on the tree so easy to go up, but when he did I shot another into his armpit, and still no reaction. I thought this bear was going to get away because I didn't have enough gun and we'd be after a wounded bear. Now he was on a long limb that was against a hill and I figured he was getting away. I shot at the right rear hip, thats all I could see. He fell with a thud. I chabered another round and got to a point where I couold see and he was dead. But the first 2 bullets had taken awhile to kill him. Maybe 45 seconds but it seemed like forever.
So the short answer is I'd use a 45 Colt if the ammo was faster, heavier bullet then what I had or use the M1 30-06 with the 5 round hunting enbloc clips.