Carry them if they make you feel better...
Buit only use them if the bear is actually chewing on you! Because at that point, you don't have much to lose!
Saw some pictures a few years back of what was left of a hiker who had emptied his .38 in the bear that ate him. Not pretty. Now, this was a HUGE bear, a big brownie, which killed (and ate parts of) two people. It was put down a few days later by several shots from a 7mm Mag BAR in the hands of a ranger.
Blacks aren't as big, or as tough, or (usually) agressive (unless there are cubs involved), but still, the best thing to do is leave the area. Let the bear have whatever it wants, as long as it isn't you or a family/party member.
Hard cast slugs in a .38 (or .357) are far from the best bear medicine, but can kill, IF you can get them where they need to go. And the head is not the best choice, unless the gun is inside the mouth!
Bear skulls are thick, and rounded, and very prone to shed handgun and low velocity rifle bullets, due to the angle. Bears also look much bigger than they are, so aiming at where you think the vitals are based on its size might not get the job done well, either. Some serious study is in order, before considering a smallbore (or any) handgun for bear defense.
Hardcast slugs are the only kind I shoot from my handguns, for several reasons. And there are different levels of "hard", as well as different levels of power they can be loaded to.
Take a pure lead bullet and dig your thumbnail into it. You can gouge a fair size notch. Do the same with a hardcast bullet and you leave a shiny spot on it. No gouge. I shoot them to keep down the leading with heavier loads in revolvers, and to keep them from being battered during the feeding cycle in autopistols.
The lead is alloyed with tin, and antimony, the exact proportions vary from caster to caster, and with the intended purpose of the bullet. "Hardcast" has nothing to do with the bullet shape, or the power level it is loaded to, it is a discription of the alloy used.