Ammunition

Ammunition is the term used for projectiles fired from guns.

Special and no ammunition required
A few weapons in the Fallout games do not use ammunition in the traditional sense at all. These are:
 * Meat Cannon (Fallout: Brotherhood of Steel)
 * Rock-It Launcher (Fallout 3)
 * Solar Scorcher (Fallout 2)
 * Vault Dweller Red Ryder BB Gun (Fallout: Brotherhood of Steel)

Clip vs. magazine
Although completely irrelevant to the game, this section explains the terminology distinctions between a clip and a magazine to better help the reader distinguish between these two commonly misused terms.

A clip is a device used to load ammunition into a magazine (most commonly an internal magazine). Such devices include the 8-round "en bloc" clip used by the M1 Garand, and the stripper clips used by the SKS carbine (the 'sister' to the more common AK-47). However, many people confuse this with a magazine, which is a device that feeds ammunition -and- encloses it. These are, for example, the curved magazine of the AK-47, which military weapon experts call a "banana clip", or the magazine of the M16 rifle. A shortened term for magazine, "mag", is also available. It would be immensely incorrect to refer to anything that does not use clips or magazines as having a "clip size".

In Fallout 3, for example, the Chinese Pistol is loaded from the top by a stripper clip. It has an internal magazine that holds 10 cartridges. The Chinese Assault Rifle uses a 24-round (or 36, in the case of the Xuanlong Assault Rifle) box magazine, the so-called "banana clip" in slang, which is an incorrect term to use.

Energy weapons can be referred to as using cells rather than magazines, as they are a battery of sorts rather than dedicated storing and feeding devices.

Improper use
This error can be easily seen in the G.E.C.K. where you can enter the magazine capacity of a weapon as "Clip rounds". The correct term would be "Magazine capacity" or "Mag capacity". Most likely, the developers just wanted to make it clearer as to what they are talking about as most people are more familiar with the "clip" usage.

In the Operation: Anchorage add-on, one of the Chinese soldiers will yell (with English subtitles) "Empty your clips! No survivors!" upon attack.

Manufactured
It is shown in The Pitt that ammo is still being produced in The Pitt and is being used by Slavers in the Capital Wasteland. The Slavers trade their latest roundup for a large supply of bullets, which are later traded to the caravans for other goods.

Technical vs. General Definitions
The above is correct for the technical terminology used, but isn't correct about the general definition. According to the general definition of the word "clip," all magazines are clips because they are attached to another device when used. All clips are not magazines because the definition of a magazine is a specific term, while clip is a much broader term. The technical definitions of magazine and clip are two different things. The general definition of the word "clip" does, however, include magazines. It is incorrect to say magazines and clips are the same things because not all clips are magazines. It is correct to refer to magazines as clips because magazines fall under one of the general definitions of what a clip is. It is only incorrect to switch the two if you are referring to the one technical definition of the word "clip" used in this one particular field. So, the G.E.C.K. use of "Clip Rounds" is arguably correct