[Mariner]

"with such power the grizzly can’t even lunge at you in its death throes?"

I don't think such a rifle exists.

I assume a lot has to do with the disposition of the bear. If he's angry and/or scared you'd want at least 50ft. 100ft would be better.

[zek157]

Doug White used a 44 Mag at extremely close range when a Grizzly attacked him after he shot & gutted a Moose.

Check out the story & pics.

https://thegreatwhitehunter.wordpress.com/the-longest-minute-terrifying-bear-attack/