Only one round is needed to stop one.
Put one in your own head that way he can stop having fun with you and just have lunch.
If all you have is a 1911 and are expecting to meat Grizzers, meat is the right spelling.
This is silly.
If you can manage to live long enough to put a round in his eye from point blank range one might do it. There's been reports of Grizzly's killed that had .357 and .44 mag bullets lodged in their skulls and bodies that had been healed over for years.
That's a question I hope to never have to find out the answer to. For that matter, how many .22 long rifles does it take? .25 acp? .380? 9mm? .38 specials? It's a question with no real answer. One lucky shot could. Twenty poor shots might not.