Let's keep things in perspective. Black bears can be anywhere from 100 lbs to maybe around 500. Realistically you will see a lot more 150 - 200 lbs bears than the 300 - 500lbs bears. I live and hike in prime black bear country (Northwest Coast and Cascade ranges) and the only large black bears I have seen were in the National Parks (Rainier and North Cascade Recreation Area).
Second, bears seem fickle when it comes to time to die. I know guys that hunt easily with a .30-30 (about same power as the .44) and others that have shot bears repeatedly with a .308 or bigger and had the bear stagger on for another 100 yds. If I really wanted to stop a bear I would be looking more toward the .454 Casull, .500 S&W, 12 ga. slugs or minimum .30-06 180 gr. but those are not the most convenient to lug around.
Third, while bears are generally evasive around humans those are not the ones you are arming youself against. Just like I don't carry in suburbia in fear of houswives and office workers (the majority of adult human species in my area). I carry for the rare example of the species that is whacked out, an out of control predator, or feels that I have threatened his/her territory. Same with bears. While only a very small percentage of black bears ever attack a human, because of their strength and size, when they do they inflict terrible damage.
A .40 beats fingernails any day. If I wanted something specifically for black bear then the .44 is pretty standard. Like a 4" Taurus or S&W or even the Ruger Alaskan. If he is stuck with a .40 then consider the 200 gr. FMJ-FP loads from DoubleTap which are clocked at 1100 fps from a 4.5" barrel.
Personally, if I am not hiking in a national park then I consider human, dog and cougar attack more likely threats and carry my G23 with the 165 gr. DoubleTap loads. If I think there is some risk of black bear then I carry with the DT 200 gr loads. Back when I lived in Washington and hiked Rainier and Olympic NP and the North Cascades where the bears I encounterd were truly huge, then I lugged a 4" Ruger Redhawk in .44 with 300 gr JFP loads.
In the Midwest I can't imagine the bears are very big and I would feel well armed with a .40 and the 180 or 200 gr DoubleTap loads to mainly take care of human or dog attack, but still be minimally reasonable for the rare bear.