I've seen it used on the Kenai River in Alaska with mixed results, 2 times the brown bears ran off and the 3rd one just continued to eat a guys salmon with a little seasoning.
My bear spray is a Glock 15 round 10mm loaded with Underwood Hardcast. That is probably the absolute bare minimum loading although I read about about a guide that killed a nasty Griz up there with a 9mm.