Scrap Metal (Fallout 3)

Scrap Metal can be traded to various different NPCs located in Fallout 3.

Walter in Megaton
Scrap Metal is desired by Walter in Megaton after completing the quest: Fix broken pipes around Megaton. He is located in the Water Purification shack during the day. He provides approx: 10 caps per 1 unit of scrap metal and the Game provides approx: 5 to 10 exp per 1 unit of scrap metal.

Note
When giving scrap metal to Walter you receive:

7xp for the 1st 6xp for the 2nd 7xp for the 3rd 6xp for the 4th This pattern continues on for any amount of scrap metal
 * Without Well Rested:

8xp for the 1st 7xp each for the 2nd through 6th one, 8xp for the 7th one, 7xp for the 8th through 13th, 8xp for the 14th 7xp for the 15th through the 20th, 8xp for the 21st.
 * With Well Rested on:

This suggests that every seventh piece of scrap metal is worth 8xp while every other one is worth 7xp. This may also suggest that you get a fractional amount of XP per piece of scrap metal, either around 7.14 if the XP is only counted if it exceeds 8, or around 7.07 XP if the amount is rounded up after 0.50 XP.

Seems as though the game is punishing you for collecting the scrap metal up and turning it in all at once.

Bugs
There is either some pathing issue, or perhaps a scripted event, that may eventually cause Walter to be found dead at the bottom of a slope to the left of the clinic. It's likely a pathing issue that causes him to fall to his death.

Winthrop in Underworld
Winthrop in Underworld also trades for scrap metal, but he will give Stimpaks or Rad Aways in return, per 5 units.

Protector Casdin at Fort Independence
Protector Casdin of the Brotherhood Outcasts is a much better option than Winthrop and is located in Fort Independence. He will trade 12x 5.56mm ammo, 1x Stimpak, 1x Rad Away or 1x Frag Grenades per 2 units.