Without ammunition, your hundred-thousand-credit death-dealing ultragun is just a fantastically expensive club, and probably not a great one at that. Ammunition is defined by type (standard, gel, AP, etc.) and caliber (5.56mm NATO, 9mm Parabellum, etc.). With rare exceptions, a firearm designed to fire one caliber of ammunition cannot fire another, and attempting to do so universally fails, sometimes dramatically.
Good old-fashioned ball or full metal jacket bullets, standard ammunition uses the statistics given in a weapon's description.
Military-grade AP rounds are designed to travel at high velocities and punch through personal body armor. Armor-piercing ammo increases a weapon's AP by +4.
These are polycarbonate, steel- or carbide-tipped, fin-stabilized bolts intended to be fired from a crossbow.
These slugs carry a shaped-charge explosive, designed to detonate and fragment on impact. Explosive rounds increase the weapon's damage by +2, but decrease its AP by -1. Explosive rounds misfire on a botch. When this happens, the weapon's damage is applied to the wielder, and the weapon itself is destroyed.
These less-lethal rounds use a hard, jelly-like substance that is a safer alternative to rubber bullets. They are often employed for riot control. Their usually semi-rigid slugs flatten on impact, disbursing their kinetic energy over a larger-than-normal area. Gel rounds inflict nonlethal damage.
These darts are intended to be fired from a dart pistol or dart rifle, and can be loaded with a variety of chemicals, from tranquilizers to poisons.
Rockets are projectiles consisting of a light metal or plastic body with stabilizing fins, a propulsion system (usually solid-chemical) and a warhead, fired from a launcher. The price listed for rockets is for each, rather than per 10.
Stick-n-Shock rounds turn a regular firearm into a taser. Rather than dealing normal damage, Stick-n-Shock rounds deliver a Stun effect.
Tracer rounds burn along the line of flight, making it easier for the shooter to home in on the target. This type of ammunition is only effective in full-auto weapons, and is loaded as every third round in a magazine. When firing on full-auto, tracer ammo grants a +1 bonus to the Shooting roll.
These darts are designed to be loaded into taser weapons.