A .22LR will kill a grizzly, and one was killed with a .410 load of birdshot up in Montana about 12 years ago (they found the wad in the sow grizzly’s nostril – it was close). A very desperate hunter killed one with a Buck 110 folding knife. However, those are all rare exceptions.
An enraged grizzly is a lot of adrenaline and muscle with claws and teeth that is moving around fast. There might be something that is a bit of a better choice than a 7.62x39mm to serve as your primary weapon of close range defense against one. I’m sure it could fatally injure one, but would it die before it shredded you or someone else? That is the question. If semi-auto is what you want, put a rifled slug barrel on a Mossberg 930.
For normal bear control, before it becomes a problem, they make specialty 12ga rounds, often called ‘bear bombs’, which are designed to try and scare bears off.