in his hand, IS still a threat, at 20 ft or so, and can easily remain so for minutes. after he's wounded, at such ranges. He is NOT, however, a threat to anyone who's at 500m, using cover, or is just head on prone, for that matter. Since you shouldn't be offering any more of a target than that, you ARE safe at such a range, from such a wounded man. So it IS ok for the rifle to have no more power than that, at such ranges. It will suffice to kill the SOB, eventually, and that's all that's really needed.