Let's be clear, you're talking black bear, not grizz or Kodiak max, right??
There is a huge difference between hunting bear, and STOPPING an attacking bear. A 240/250gr SOLID bullet at 11-1200fps is plenty to do the job, but YOU have to get it in the right place. And, if you're talking about stopping a charging bear at short range, count on only getting one shot at a small (vital spot) moving fast and not in a straight line.
Plus, the bear's vitals are NOT where most think they are. Study their anatomy, and you'll see what I mean. Mr Bear wears a baggy suit, covered in fur, which frequently leads to misidentifying where the vitals actually are.
I am not a fan of uber heavy bullets. Despite them being all the rage on the internet, I don't have any use for 300gr+ slugs in either .44 or .45 pistols. Get them up to speed and yes, the energy and penetration numbers are awesome. BUT, there's no free lunch. Recoil matters, and matters a lot if you're hoping for a fast second shot. And, black bears aren't buffalo. You don't need 3 feet of penetration capability before reaching the vitals. nothing wrong with a bullet that does that, but if it does it at the cost of being able to rapidly fire a second shot, its not a good choice for DEFENSE.
The best bear defense is the Miyagi defense ("no be there"), but failing that, your brain, using your eyes and ears, and FEET to avoid a confrontation. There is no "stand your ground" rule with bears unless you are protecting someone else. NO amount of property is that important, only human life. Retreat. NEVER RUN!!! (it just attracts their attention).
Bears are not impressed by the caliber of your gun. they are not usually impressed by a gun, at all. No bear thinks "oh my he's got a .500, not a puny .45Colt, I better leave...."
Many decades ago, Elmer Keith wrote about how any "decent" handgun would kill a bear, if you kept your nerve. He was referring to .38 cal and up as "decent" handguns, and the keeping your nerve part was vital. Every bear opens its mouth when it attacks. Shoot through the mouth to break the bear's neck. Elmer never claimed you wouldn't get clawed or "chawed", only that if you kept your nerve (made the shot) you would kill the bear, and win the fight.
Get that Ruger .45 or what ever it is you want, and be happy. Learn to use it well, and you'll be safe. The gun and load are important, but they are much further down the list than it seems at a glance. Too much gun is just as bad, maybe even worse than not enough.