Bear aren’t any harder to kill than a whitetail. I like faster better than slower caliber. A 30-06 is perfect, how about a Ruger American? Not a big fan of plastic magazines but the rifle is accurate. I believe the sportsman’s guide has 270’s for $279. Years ago I sat over bait in Canada at about a 120 yards. Shot two bear with a 45-70 guide gun. Both bear ran with no blood trails and were never recovered. I have video of the bullet going between the shoulder blades of one while it was feeding out of a 55gal drum like the bullet was flying in slow motion. If it was going slow enough to see no wonder it had no knock down powder. I was using Winchester factory ammo in 300 or 405 grainers if I remember. Not a big fan of the shoot today and find tomorrow caliber. If it’s a close shot under 50 yards then yes. Guarantee if I took my trusty 30-06 with the first bear wouldn’t have went anywhere or very far. I have an American 450 bushmaster that is basically the same undated version of the 45/70 imo and I’m slowly weaning myself back with. I shot three deer with a Ruger 77/44 last year. One ran 140 yards, one a 100 yards, and the third dropped all with double lung shot placement. A 265 grain cast hollow point loaded at 1750 FPS. Massive destruction and complete pass throughs. Not a big fan of slow velocity calibers for big game anymore. I do less tracking with bow shot deer. I’d rather have soft bullet traveling over 2500 FPS with a lot of kenitic energy transfer imo. I watched 13 black bear get harvested one season. From 44 mags, 45-70’s, 12 gauge slugs, to 30-06. They all dropped out of the trees where dogs had them pinned and ran. The only ones that didn’t run where shot with 300 RUMs. Shot mine with a swift scirocco and my buddy with a 180 gr nosler ballistic tip. The next time I was drawn 9 years later I used a 200 grain nosler partition. The bear did a summersault at the bait pile, got up and made it 45 yards before expiring with a sparce blood trail. What ever you choose pick a bullet that will exit and make the biggest exit hole for a good blood trail if needed. If black bear aren’t shot in the backbone or in the head the odds are they are going to travel some distance after being shot. Shot another with a 19 3/16” skull using a Rocky Mountain gator 100 broadhead. Complete pass through right through the lungs and slit the heart. My arrow was solid red with good and sticking in the sapling right behind it. The bear made it 150 yards with no blood trail. Realistically anything .243 or bigger over bait at rock throwing distance because it’s not going to matter much. Just use a heavy for caliber bullet to get a pass through. The 45-70 thing...I did the same. Bought the gun for the hunt and practiced all summer. Should have stuck with my 2750 FPS 180 grain core lock load over the 1600 FPS 4570 load and I would have brought home a bear imo without a doubt. The slow bullet acted like an arrow at that distance with no energy transfer or expansion and sailed right through it and the bears fat clogged up the hole. A fast expanding, fragmenting bullet will help slow the bear down for less travel time before expiring.