Okay Here's My 2 cents on, THE Best, Rifle, Pistol or, Shotgun, FOR,.. a "Charging",.. Grizz , Polar or, Brown Bear,..
I'd Go with an, "African, Double Rifle" in, .375 H& H, . 404 Jefferey, .458 win. or, .416 Rigby with Thick Jacketed SP Bullets, as they Worked, VERY "Well" on Charging,. Lions, Tigers, Cape Buffalo and Elephants ! ( You Still gotta, shoot "Straight" !! ) Those Big Bore, Double Tap's, "Worked" ( Usually ! ).
One of, my Customers ( years ago ) Shot, a Polar Bear with, 3 Shots out of, a .300 Weatherby MkV ( 180 gr. ) and said that, His Guide Put One, in Him, too from, a Win .375 H&H ( He WAS,. a "Toughie" ! ) First Shot, was in Upper Chest as bear was standing and "Looking" around at, 80 Yards and it got, the Bear to,"Charge". He said that, He was shaking so Hard when the Bear finally Piled Up, Dead at, 20 Feet that, he couldn't light, a Cigarette for, quite a while ! The .270 win, .280 rem, .308 win. or, .30-06 with, Heavy weight Partitions, would probably, "Get, the job Done", in the RIGHT "Hands" shooting for, the Mouth / Nose, area ! ( They Just wouldn't Be, My First, "Choice" ! )
I've always Felt, pretty Comfy with, My .338 Win Mag., Mk V Bolt action and 210 Noslers, in Grizz country !