I've taken about 10 black bears (in various color phases) over the years. By sheer coincidence none were ever taken with a muzzle loader.
I would usually do a spring hunt and if, when I went out, it was pouring down rain I would take something other than a muzzle loader. Or in some instances I would be 'experimenting' with something new. (i.e. 35 Whelen)
Except for the Whelen (.35 caliber with 250 grain bullet) and a military '03 Springfield (.30 caliber with 220 grain bullet) all the rest were taken with black powder single shot cartridges. (i.e. .45-70, .40-65, .45-90) The bullets were always my own cast bullets and, as with the .40-65, from a mould I made myself.
One really large black bear was taken with a .22 handgun but it was not my original intention. And like the .35 Whelen, was almost forced upon me.
Black bears are not hard to kill when shot in the 'boiler room'. To my knowledge, the only bears that are difficult to kill are the Northern bears...Griz, Brown, Kodiac, Polar, etc. I don't consider myself an expert by any means, but hunting bears, to me, is no more difficult than getting a good Mule Deer buck. Elk, on the other hand, can be very difficult with the ranges at which we (MLs) normally hunt.
Without trying to offend anyone, I would say that inline hunting with a bullet, whether you use black powder or not, is not the same as hunting with a roundball and iron sights . The fact that you are using black powder instead of smokeless is meaningless. A .50 caliber black powder load, using a bullet (or sabotted bullet), and a scope is no different (for the first 100 yards) than a .308 Winchester.
But the fact is that I've killed a few black bear, eaten all of the meat, and used the claws, the hide and the lower jaw. They were not difficult to kill or to sneak up on. I cannot count the number of black bear that I have enjoyed a 'mutual surprise' with to the near fatal heart attack of both. Northern bears are another proposition and I leave someone else to give an opinion of those.
I stopped hunting Black Bears about 14 years ago and would only resume now with a muzzle loader. As a matter of fact I just might try it with my smoothbore but they just aren't that much of a challenge unless you hold out for record book size.
Voyageur