I would have to echo others that mixing blanks and live rounds seems like a bad idea to me. It just looks like a recipe for a bad outcome. If you want non-lethal bear protection, carry bear spray. If you want to carry a firearm for bear protection then it should be loaded with all live rounds.

I have had some very mixed experience with warning shots to scare bears. Once on Kodiak we had a bear snorting around in the alders behind camp. One guy fired two or three rounds overhead from a 44 mag and that seemed to do the trick. We had no further trouble from that bear. In this case, blanks as noise makers might have worked as well.

On the other hand, one time two of us were sheep hunting in the Wrangells. My buddy had shot a Dall Sheep earlier that day, and we were packing the meat and trophy down the mountain. The biggest black bear I have ever seen stepped out of the brush in front of us. With backpacks full of sheep parts we smelled like tasty morsels! It was open season on black bears in that unit, so we could have taken him as game. However, we were both exhausted, already had packs heavy with game, and we still had miles to go to camp. While my buddy kept him covered, I fired a 30-06 round over his head. The bear hardly flinched. I fired a second shot into the dirt in front of him, which kicked up a lot of dirt and fine gravel into his face. That finally got his attention and he ran off. In this case, blanks probably would not have worked. Even though we didn't shoot the bear, it took a live round kicking up dirt to make the point.

EDIT: I don't have data to prove it, but I would strongly suspect that in the above cases, the 44 Mag and the 30-06, both with live rounds are louder than a 357 blank.

Speaking of bear spray, today's paper had a story of yet another successful use of spray.