I Called in two bears in Az. in the 4 Corners Area which is just lousy with bears and lions. The area is very rugged and we hunted off of mules.
One guy with me was a retired navy caption that had seen a lot of active duty in Korea. The bear called in with him was probably a two year old, not very big. The bear sounded like a volkswagen coming through the woods, and as he got near, he was clacking his teeth looking to take a wounded animal away from another predator. As he approached us at a dead run at about 50 yards, I stood up, threw off my face mask and started screaming waving my hands. The bear cartwheeled and ran off never missing a pace,
My hunting parnter was scared to death, and he informed me he had heart problems and could not take that kind of excitement. Two weeks later I called him to see if he was ok. He had settled down and was glad to hear from me saying how much he had enjoyed the mule ride. I told him that a lion had been spotted outside a trailer park near Coolidge and we needed to go take him. He told me that he simply could not take that kind of excitement anymore.
Shotgun with buckshot or slug is your best chance. If you want a back up gun that is a pistol, then a 44 mag or even better a Ruger Black Hawk loaded with 300g hot loads is best, and you had better be a crack shot.
If all you have is a 45, then the Corbon 230g fmj at 930 fps is what I would use, you need to break large bones and penetrate to the vitals. I would not use a HP intened to give good expansion on humans. 250g SWC hard cast would be great also.
Bears have a great nose, and if they smell a human, they are gone. Coming across a sow with cubs is probably your only danger.
If you have not tried calling bears, give it a try. They will respond to a raspy coarse call, put out socks filled with two cans of sardines packed in oil. Always be aware of wind direction. Wear boots that have not seen concrete at the gas pump.