What good are guns without ammo? You'll find a wide variety of ammunition types throughout System Shock 2, and several weapons draw from the same pool of ammo, or have multiple ammunition types available, with different effects. Below you'll find a list of all of them.

Standard Bullets Standard Bullets
Used With: Pistol, Assault Rifle.
Description: Probably the most common ammunition in the game. This ammo is the standard issue for both the Pistol and Assault Rifle, and deals decent damage. However, given that Anti-Personnel and Armor-Piercing Bullets are more effective against different enemy types, Standard Bullets are best used early on when special ammo is limited, as a backup, or spent on cannon fodder.

Anti-Personnel Bullets Anti-Personnel Bullets
Used With: Pistol, Assault Rifle.
Description: This ammo works excellently when fighting Annelids and part-human enemies like Hybrids. It's fairly plentiful, and generally far more useful when facing soft targets. Just avoid wasting it on armored enemies, like robots.

Armor-Piercing Bullets Armor-Piercing Bullets
Used With: Pistol, Assault Rifle
Description: As the name implies, this ammo is perfect for taking down mechanical foes. However, it's also the most rare type of bullet available, especially early on, and even by the end of the game you may not have enough to fully fill an upgrade Assault Rifle's clip. Use these against the tougher robots you come across, like Military Bots, rather than against weaker enemies like Protocol Droids. Of course, they're also a lot less useful against organic targets, so avoid firing at the Many with these if you can.

Rifled Slugs Rifled Slugs
Used With: Shotgun
Description: The Shotgun is a go-to for much of the game, and Rifled Slugs are its go-to ammunition. They are reasonably accurate, and do decent damage against armored and soft targets, and are more than plentiful. However, the Shotgun does not have an armor-piercing equivalent, so you may want to consider using it as an anti-personnel weapon and loading it with Anti-Personnel Shotgun Shells instead.

Anti-Personnel Shotgun Shells Anti-Personnel Shotgun Shells
Used With: Shotgun
Description: Somewhat less common than Rifled Slugs, but this ammo is probably what makes the Shotgun worth using. It can do incredible damage point-blank to just about anything made out of flesh, owing to the large number of pellets fired. One-hit-kills will be a frequent sight when you've got your Shotgun loaded with these, but don't try using it at range, or your ammo will go to waste.

Fragmentation Grenade Fragmentation Grenade
Used With: Grenade Launcher
Description: The standard ammo type for the Grenade Launcher, Fragmentation Grenades are more common than other types, and all-around effective for most purposes. Use it against clusters of weaker enemies, or toss a few towards a Military Bot to give it something to think about.

Incendiary Grenade Incendiary Grenade
Used With: Grenade Launcher
Description: Fire! Burn! Mwahaha! While nearly useless against the mechanical enemies you'll find during your stay aboard the Von Braun, Incendiary Grenades make extremey short work of just about anything living and breathing. Just be sure not to be nearby when one of these goes off.

EMP Grenade EMP Grenade
Used With: Grenade Launcher
Description: EMP Grenades do huge amounts of damage to mechanical enemies, but are ineffective against anything else. Save these for the big guys - Security Bots, Missile Turrets, etc.

Proximity Grenade Proximity Grenade
Used With: Grenade Launcher
Description: Proximity Grenades do similar damage to Fragmentation Grenades, but act as land mines, going off whenever an enemy comes near. Great for laying traps, guarding an area, or just tossing at the floor and waiting to see who comes knocking.

Disruption Grenade Disruption Grenade
Used With: Grenade Launcher
Description: Ah, Disruption Grenades. One of the rarest ammo types until the very late game, Disruption Grenades have a small blast radius, but do incredible amounts of damage. Use these against powerful single targets to take them down instantly.

Prisms Prisms
Used With: Stasis Field Generator, Fusion Cannon
Description: You'll start to see lots and lots of Prisms around the Command deck, though you may encounter them earlier. The Stasis Field Generator and Fusion Cannon are ammo-hungry weapons, so it's well enough that you'll be swimming in them by the late game. As it's the only ammo type for these two guns, there's no upsides or downsides associated with it.

Small Worm ClusterLarge Worm Cluster Worm Clusters
Used With: Viral Proliferator, Annelid Launcher
Description: If you've spotted piles of worms on the floor aboard the Von Braun, you've likely passed them by assuming they're mere curiosities. Not so. If you've got a Small Beaker or Large Beaker, you can use it to pick up those worms, and you'll have a Worm Cluster to power your Viral Proliferator or Annelid Launcher. Unfortunately, this is the most rare of all ammo types in the game, and you may be better served by using Molecular Duplication to keep your supplies up than hunting them down yourself. The two sizes of Worm Cluster relate only to what sized beaker has been used to pick them up; there's no difference in damage quality or type.