I have never shot a black bear, though have seen a number shot. I do spend a bunch of time in the woods around them though. This is in MN and WI not out West. Even in mostly dense woods my bear encounters are generally at a distance where I would rather have a scoped rifle than a lever action. Not there is never a surprise up close interaction but its a low percentage of sightings. I would think this would be even more true out there.
I would lean toward a relatively short barrel rifle with a relatively low power fixed scope as being ideal. Caliber would not matter much to me.
It would certainly matter where you’re hunting, and your hunting strategy, and the time of the year. I would probably never hunt black bear anywhere I’ve seen them with a 45/70, if I was hunting them in close quarters I would rather use my bow or a revolver (either weapon as well as a 45/70 would be limiting my range on purpose to make the hunt more difficult)
If I want to give myself the best chance of killing a bear, I’m using the same rifle I would use for deer. Especially in the spring, I would want as much range as I am willing to shoot, because it’s very common to spot them at a distance, and it may take a long time to get sub 100yds from them, and in the spring, they don’t stop moving and often disappear pretty quickly… if you spot one at 500, you may be able to close to 250 pretty quick, but to get to 200 or less, it might take a long walk to get to the bear’s side, and if you have good wind across from it, you probably won’t once on the bear’s side.
Bear (especially in the spring) are often feeding on very steep slopes (like landslide chutes or rocky bluffs) so even if you get on the bear’s side, and have good wind, you still might not be able to see one on the same side due to the lay of the land.
Fall bear a short range weapon makes a little more sense, a bear feeding in a berry patch is more likely to stay put for awhile and give you time to get close, but it is still beneficial to have more range, because a bear that’s in a big berry patch might be hard to see from its level, and there is usually a way to get elevation and have a better angle, but it might not be a close shot
I don’t like the bullet choice that much with a 45/70 either, you have a slow heavy bullet that is either a flat nose or very thick jacket hollow point (like lever revolution) and you will be stuck to a pretty narrow wound (especially with a flat nose hardcast or soft point)
I would much prefer a match bullet moving over 2k fps and the destruction they offer. Bear don’t always bleed well, and they retreat into the worst place they can reach. They die in the absolute worst places possible, and penetration is low on the list of priorities hunting black bears, they are softer than deer, so doing damage is more important than penetration with bear, especially where the vitals sit on bear… on a broadside shot, your bullet will be nowhere close to any bone besides ribs.
Depends on how bad you want to kill one, is the method or a filled tag more important?