Bear? What kind of bear? Alaskan brown (Grizzley)? There is no pistol made including the new 500 S&W that is adequate for stopping a Griz. Guides in Alaska typically carry rifles with over 3000 ft pounds of muzzle energy and heavy strong bullets (450 Marlin, 375 H&H or 12ga Brenneke slug) for Mr. Griz. Back to your question about a 45acp for bear, I'd prefer a 10mm, 41 or 44 magnum thank you. The 45 acp was designed as an anti personnel short range last ditch weapon and was never intended to deal with large dangerous game.