I killed my bear this spring doing exactly that. 298yds, (quick drop average gun, yardage -2 =dial) 298yds-2 =1MIL.
I saw the bear headed toward an opening. I ranged the opening just as he came out sooner than I expected. I was sitting on a stepped ledge. I had just enough time to turn around, grab my pack, plop it in front of me upright, dial 1 MIL, flopped the rifle over the pack and got the crosshairs on him. just as I did, he stopped and stood up. I shot him in the chest and hit him about 2" right of poa.
I saw the shot was good in the scope and he went down. He moved a little and I put a second shot in him but he was dead.
From when he came out to the second shot was about 25 seconds, maybe 30.
I could have just held one MIL and saved a few seconds.