Weaponsmith

 is a Fallout 3 achievement on Xbox 360 and PC and a trophy on PlayStation 3.

It is granted for constructing one of each custom weapon. Those are:
 * Bottlecap Mine
 * Dart Gun
 * Deathclaw Gauntlet
 * Nuka Grenade
 * Railway Rifle
 * Rock-It Launcher
 * Shishkebab

Bugs

 * Sometimes after you have made each weapon, the game doesn't give you the achievement/trophy. However, this may be due to finding one of these weapons rather than actually constructing it.