Fallout: New Vegas weapon mods

Overview
Several of New Vegas's weapons can be modified with mods.

There are multiple weapon mods for some weapons, and a maximum of three weapon mods can be attached to any one weapon. Once any weapon mod is attached it is permanent, however there are multiple of each mod in the game, so be wise in what you want to attach. For example, while an extended magazine is almost always beneficial, a scope has pros and cons. It may increase maximum range, but making it harder for close combat.

Mods are attached by having both the weapon and the mod in your inventory, then going to the weapons page on the Items tab within your PipBoy, highlighting the weapon you want to mod, and looking to the right of the info pane to see what button or key to use to open up the mod screen for that weapon. After you have selected a mod, the weapon name will have a + after it to show it has been improved. Modding a weapon also increases its value.

Unique weapons cannot be equipped with weapon mods. While unique guns usually have better base stats, Obsidian Entertainment (no not Bethesda Softworks, they didn't develop Fallout: New Vegas, they just published it) introduced this inherent drawback to balance out unique and normal weapons and make the choice less of an obvious decision and more of a preference.

There are currently 11 vendors who offer weapon mods, which their inventory of mods seem to change with time, in the Mojave Desert:


 * Alexander, 188 Trading Post (Need at least 40 guns skill to pass challenge)
 * Great Khan Armoror,
 * Blake, Crimson Caravan Camp
 * Vendortron, Gun Runners
 * Gloria Van Graff, Silver Rush, Freeside
 * Dale Barton, The Fort
 * Chet, Goodsprings
 * Michelle, 188 Trading Post
 * Knight Torres, Hidden Valley
 * Old Lady Gibson, Gibson Scrap Yard
 * Cliff Briscoe, Novac