Ammunition

Ammunition is the term used for the projectiles fired from guns.

Fallout, Fallout 2 and Fallout Tactics
Some guns can use multiple types of ammunition, some of the most common variations being Armor Piercing, Full Metal Jacket and Jacketed Hollow Point.

There are three major statistics attached to ammunition: Armor Class Modifier, Damage Resistance Modifier, and Damage Modifier.

''Note: The Fallout 1 engine does not implement the ammo modifiers, so there is no difference between JHP and AP ammo. (explanation thread)''

Fallout 3
Unlike previous games, in Fallout 3 there is only one type of ammo available for each caliber.

Clip vs. magazine (HOW IS THIS RELEVANT TO FO3??!!)
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 many people mistakenly 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 DLC, one of the Chinese soldiers will yell (with English subtitles) "Empty your clips! No survivors!" upon attack.