Fallout: New Vegas ammunition

Ammunition or ammo is used by weapons $$ The Pip-Boy 3000 menu displays ammunition of any given type by the combined weight of all rounds of the same type and not the weight per round.

Other

 * Note: Camera film is classed as a form of gun ammunition.

Ammo Boxes

 * Note: Weight only applies while playing on Hardcore mode.
 * ¹ Compatible with weapons that use 5.56mm Rounds.
 * ² Compatible with weapons that use .357 Magnum Rounds.

Named vendors
These are vendors carrying large amounts of certain ammunition types.
 * .308 Round: Daniel Contreras at Camp McCarran and Quartermaster Bardon at Hoover Dam.
 * 12.7mm Round: Daniel Contreras at Camp McCarran and Quartermaster Bardon at Hoover Dam.
 * 12 Gauge Round: Quartermaster Bardon at Hoover Dam.
 * 25mm Grenade, .50 MG: Vendortron at Gun Runners, Alexander at 188 Trading Post, and Quartermaster Bardon at Hoover Dam.
 * 40mm Grenade: Cliff Briscoe at Novac, Vendortron at Gun Runners, Lacey at Mojave Outpost, Boomer munitions manager at Nellis Air Force Base, and Quartermaster Bardon at Hoover Dam.
 * Flamer Fuel: Chet at Goodsprings and Johnson Nash at Primm.
 * Great Khan armorer at Great Khan armory has large quantities of all ammunition except Missiles and Flamer Fuel.
 * Rocket: Gun Runners Vendortron.

Loading
To load different ammunition, go into the Pip-Boy, scroll to the "Ammunition" section and select from the list any compatible ammunition type for the currently equipped weapon. Outside of the Pip-Boy menu, pressing hotkey "2" on PC or "Up" on the Xbox or PS3 d-pad will change ammunition; this will also cause the weapon to be reloaded with the new ammunition.

Bugs

 * Occasionally when switching between types of ammunition for a gun, the loaded ammunition may become "stuck" and not allow you to switch.
 * To correct this, you need to switch over to another weapon that is hotkeyed.
 * Alternatively, you can drop all ammunition of the currently loaded type. The gun should then switch to the other ammunition type and then you can pick back up the first set of ammunition.
 * Alternatively, you can unequip the weapon in the Pip-Boy, then change ammunition types.
 * When adding large amounts of ammunition using the console command, the game may crash. This is especially evident when adding .50 MG Incendiary rounds.
 * When transferring ammunition to a companion in Hardcore mode and you get a message that the transfer will overload them (which is correct), try reducing the amount you're giving them at once. For instance, Boone might not like you giving 200 Microfusion Cells to him at once, try 20 or 50 at a time. You can keep trickling them in at this reduced amount until they're all transferred. You can then proceed to transfer in different ammunition types in the same trade session, but once you exit, you'll have to take some weight off him to bring him under 220WG to 'overload' him with ammunition again. Note: On the character wheel, it will still display his maximum full weight (220/220 WG) though what he's truly carrying could now be far exceeding this.
 * While using .22LR, Plinking ammunition in Vault 3, the repercussion sounds of bullets won't stop until you have exited the Vault.
 * While using special ammo, if the magazine capacity of the weapon you're using is greater than the number of default weapon rounds you have in your inventory you won't be able to reload past that number after fast travels and savegame loads. Usually, happens when breaking down default ammo to make special ammo. The bug will persist until the number of default weapon rounds in your inventory surpasses the magazine capacity.

Behind the scenes
Joshua Sawyer, Paul Fish and Mitch Ahlswede made the decision to expand on the bullet and shell casing models in Fallout: New Vegas, compared to limited ammunition models in Fallout 3. During development, they experienced a bug where the case would always render under the gun in V.A.T.S., which they fixed. Sawyer stated that the minor details relating to ammunition models made V.A.T.S. feel better to him personally.