sorry about the answer i just gave,thought i was still on the new vegas fallout.i haven't played the reg fallout 3 for awhile,but from what i remember it was a basic pistol
Lincoln's Repeater is excellent -- at the Museum of History. I just gave it to Hannibal the Slave at the Lincoln Memorial and have regretted it ever since.
after you do the quest "waters of life" head to deathclaw santuary (when you are stong enough to survive) and pikc up "jack" tears anybody who gets too close into ketchup looking paste
Ol' Painless. You can run to the Republic of Dave as soon as you get out of the vault and you'll likely only encounter a couple dogs and a few Raiders on the way. It uses common ammo and is repaired by common hunting rifles.
Lincoln's repeater is surprisingly easy to find (It's still a job though). You have to kill a crap-ton of feral ghouls to get it (bring lot's of ammo) but it's well worth it. I find a combat shotgun to be good against ferals.