One of the features added to New Vegas is the ability to custom modify certain base weapons. While in Fallout 3 this was limited to the creation of custom weapons, New Vegas takes this a step further by allowing the creation of weapon variants based on basic weapons by adding weapon mods. The addition of a mod to a weapon will permanently increase the overall monetary value of that weapon by the value of the mod, even if the weapon is completely broken at the time it is applied.