Bigger is better ,that is true,bears need to be dropped,and dropped quickly,for 2 reasons where they want go in a thicket and to stop a possible retalatory lunge or charge which is possible with even smaller black bears, I've used 6.5X55 with heavy bullets(160gr.) ,30/30, 06
303 But I now use only 45/70 GG and sometimes my Brown Bear cartridge 375 H&H cartridge , if its in the swamps where the Blackies get large and shots(in clearings ) can get 200yd.s or so the 375 H&H really shines there.
I had a hunting pal rag me over my 375 H&H once ,telling me it was overkill.The next day he ate his words when I dropped a 650 pound Blackie from over 185 yd.s out ,a shot he would had to pass up even with his 06.