The Bear Awareness Course I received when working in Forestry by a fellow named Shelton (from Alberta) stated the very best bear protection came from a short 12 bore loaded with slugs.
Buckshot was deemed to be nearly useless on grizzlies although slightly better on black bears. I know from experience that is sucks on large black bears. Slugs do work and work well.
The instructor noted that spray, if applied at 12' or a little less would stop a charging grizzly, whereas shooting it at that same range, it would run you over, whether it was dead or not, due to momentum.
He also noted that in a determined charge, the head is low as-is the bear's body. A "heads-up" bear is likely making a false charge. Note the word "likely".
I had 2, 11 round mags for my .45, back in the 70's, but they were kind of ridiculous, sticking 3" to 4" the handgun.