Anything that can cleanly take a whitetail deer will also do the job for a black bear.
And that includes the "lowly" .30-30 and 12ga (even with buckshot). In fact, back when I lived in the NE, I hunted in areas where buckshot was NOT legal for deer, but WAS LEGAL for black bear. GO figure...
If anything, particularly where you live, you are bordering on overgunned with a .300 Weatherby.
The thing with black bears is not the power needed, its the precision. Black bears are not as "big" as they seem. While the bear's vitals are in the same general places as all mammals, the bear's loose skin, fur, and postures make it easy to misjudge where that "right spot is". Study the bear for a bit, and get familiar with where the vitals are, actually, compared the where your mind will think they are. The difference isn't much, but can be enough to turn a clean kill shot into a wounded bear hunt.
Also, avoid head shots, besides being a small rapidly moving target, the bear skull can sometimes deflect/shed even high velocity bullets, if the combination of impact angle and skull bone curvature are just right. That has little to do with the power of the round and a lot to do with angles. A rifle round that glances off a GI helmet with one impact angle, easily punches through with a different angle. Same principle.
Black Bear are not armor plated giants, but you have to know the bear, AND make your shot.