Fallout: New Vegas ammunition

Ammunition or ammo is the term used for expendable ordnance material used in charging firearms of all kinds; as powder, balls, shot, shells, percussion caps, rockets, missiles, energy, etc. The purpose of ammunition is to project force against a selected target or area.

Currently 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 actually classed as a form of gun ammunition.

Ammunition 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.

Notable 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 shotgun shell: 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
 * HE and HV missiles: 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, drop all ammunition of the currently loaded type. The gun should then switch to the other ammunition type and you can pick the first set of ammunition back up. *Confirmed*
 * In reference to the above statement, you cannot change ammunition types (by hitting up on the D-Pad), when the weapon is holstered. Additionally you might not be able to change ammunition types via pip-boy on an equipped/holstered weapon. You can unequip in the pip-boy, then change ammunition types. *Confirmed, but not sure this is an actual bug.
 * if you switch over to another weapon you have hotkeyed it will stop the bug mentioned above.
 * 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 lumping 200 microfusion cells on him at once, so try maybe 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.

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