Doc;
Welcome to the campfire!
My fav rifle for black bear is in .45-70. I've had several versions of the Marlin, a couple Rugers and an NEF(single-shot).
But, I have to be disagreeable (I hate that!)with some of my good buddies here on this thread...
What size bear do you anticipate? How far the shot? Over bait, or spot-and-stalk? Thick brush nearby or open areas where you can see and track the bear if he doesn't stay where you shot him/her? And many, many other questions should be considered.
I'm not a "pro" but just about in that I hunt bear every year, have taken a fair share, was taught for eight seasons by a "pro", have been baiting on my own for 15 seasons, have written a manual on baiting bear/hunting them, and currently have bears coming to my baits. That's just a brief summary of my personal interest and involvement with black bears in Central Ontario.
Let's just say that 50+ years of hunting has found it's culmination in studying bears, researching them and dedicated hunting of them over the past couple of decades. It occupies a lot of my time, thinking, planning and expense.
So, I do have some ideas when it comes to black bear and their clean termination!
Because I'm not a casual hunter of blacks, I bait several areas each year and observe them, but only shoot one every third year. The black bear deserves utmost respect, and while I have immense confidience in the .45-70, if I were you I'd go with the best ammo available. As to factory loads: that's Garrett! Google Garrett Cartridges online. Then there's also Buffalo Bore Ammunition. These bring about the best out of the Marlin in factory fodder. I'd forget Hornady or Remington.
Just my thoughts and experience, and the last bear I shot was trophy quality, flattened in his tracks at 70 yds by a 465gr hardcast handloaded from a NEF Handy-Rifle at 1900 fps! That was three years ago. I'm do again!
Bob
www.bigbores.ca