I thought that the current hunting rifle and Ol' Painless weren't good enough for end game or even middle so I made unique Hunting rifle which has damage increased. I added small QUEST too.It would be too easy elseway.

Video walkthrogh of the quest: http://www.kleep.com/Video-Games/Fallout-Three-Mod-Ol-Painful-Walkthrough.896701

The rifle has about ~50 dam when at 100% condition with small guns at 100. I think it's pretty balanced now so it's not cheat item. It's Ol' Painless with just changed name and dam.

In order to start the quest go to Jury Street Metro Station you should find Jackson there.

If you don't want to do the quest just go to vault 101 entrance(inside) and it should lay on the ground there.