Weapons are prone to damage and unreliability if struck severely enough or exposed to extreme or abrasive conditions.

Firearms & Other Ranged Weapons

Weapon unreliability causes a cumulative 5% chance for weapon malfunction and/or failure. The first source of unreliability causes your weapon to suffer a malfunction on a roll of 1. A second source of unreliability causes the weapon to malfunction at a roll of 1 or 2 and so on.

Common Causes of Weapon Unreliability

Age: Age and heavy use can render a weapon unreliable. A weapon unreliable through age can only be fixed via a complete overhaul. Overhauling a firearm is a complex repair check.
Damage: Any firearm that has taken 1 hit point or more of damage is unreliable. This can be solved by a simple to moderate repair check.
Environment: A steamy jungle, dusty desert, or similarly rough environment can make a weapon unreliable. During extreme weather conditions firearms will require an extra half hour of special maintenance each day to ensure weapon reliability.
Immersion: Immersion into water or other liquid can cause a firearm to become unreliable. The majority of the weapon must be immersed in water, so even heavy rains are unlikely to cause weapon unreliability. This unreliability is removed via drying the weapon out, either in one minute by disassembling the weapon and drying it by hand(a repair check) or by giving the weapon six hours to dry by itself
Unreliable Ammunition: Ammunition can become unreliable if damaged, improperly maintained or exposed to harsh environment and weather conditions. This type of unreliability is fixed simply by discarding the unreliable munitions and using non-damaged ones.
Unusual Ammunition: Conventional ammunition does not cause unreliability, but some exotic forms, such as AET ammo and some types of shotgun shells, cause unreliability. Using standard ammunition removes this cause of unreliability.
Improper Maintenance: If a weapon isn’t maintained properly through regular cleanings and general routine maintenance it will become unreliable. This source of unreliability is removed with the application of general maintenance and cleaning(a simple repair check)

Melee Weapons

If melee weapons(swords, axes, knives, clubs etc) are not properly maintained through regular sharpening, and general weapon care and maintenance they will begin to wear down and lose efficiency. To prevent this regular weapon care must be applied, especially after heavy use.

Bladed Weapons: Failure to maintain an edged weapon causes it to lose sharpness resulting in a cumulative -1 to damage and reduces the weapons overall durability slightly.
Blunt Weapons: Failure to maintain a bludgeoning weapon results in loss of durability, and increases the likelihood of the weapon being sundered in combat
Whips and Chains: Failure to maintain a whip causes unraveling resulting in a -1 to damage and accuracy