Go to Evergreen Mills, if you haven't been there before you will have to fight alot of raiders and there's also a super mutant behemoth.

After you kill all of them go inside the Evergreen Foundry and there will be a good amount of guys in there, but you will find a guy name Smiling Jack and it shows him as a good guy.

Yo can kill him and it won't give you bad karma andif you have the lawbringer perk you will get a finger. If you kill him get his key and open his locker. You will get the terrible shotgun in perfect condition.