The hunting shotgun, loaded with slugs does more damage than a sniper rifle, plus you get -15 DT from the shotgun surgeon perk. I can pop the head of almost anyone with one shot from the thing.
It's -10. Against people not wearing power armor or combat armor, this is good. Looking at the charts, Power armor combat armor has 20+ DT. If it looks like metal armor, it's a waste of time. If it doesn't look like some form of metal armor, blast away. While some of the non-metal armor is 12 or 13 or so, most is exactaly 10 and some are under.
If they look like they have armor that would reflec the pellets of a shot gun, they likely will, even with this perk. Still useful for head shots, which is kind of what this is names after.