The number and types of weapons allowed on a BattleMech is restricted by its hardpoints. All weapons have the following characteristics, with additional information in their respective sections.
- Damage: the amount of health removed from the target if hit when within the weapon's optimal range.
- Optimal Range: the maximum distance which the weapon deals full damage to the target.
- Max Range: the maximum distance which the weapon deals any damage to the target. Damage drops linearly from optimal to max range.
- Minimum Range: some weapons have special rules if targets are within this range. See below.
- Cooldown: the amount of time between firing a weapon and being able to fire a second time.
- Heat: the amount of heat generated every time the weapon fires
- Slots: the size of the weapon
- Tons: the weight of the weapon
- Velocity: the speed with the projectile travels across the battlefield. Laser weapons are instantaneous.
- Impulse: the kinetic energy imparted on the target, causing cockpit shake
- Health: the amount of critical damage the weapon can withstand before being destroyed
Ballistic weapons deal kinetic damage. They are the heaviest weapon type, have medium projectile speed but generate the least heat relative to their damage. They require ammunition, which may be expended before the battle is over or explode due to a critical hit.
Energy weapons deal damage over time. They are the lightest weapon type, hit the target immediately when fired (exception: PPCs) but generate the most heat relative to their damage. They do not require ammunition, but have an increased need for heat sinks.
Missiles are cluster weapons that travel much slower than ballistic weapons. They are a middle ground with weight and heat, but the missiles spread over range. Some missile weapons can strike beyond line of sight. Some missiles have a minimum range, and most missiles do not have a damage reduction over range. They require ammunition, which may be expended before the battle is over or explode due to a critical hit. See Lock On Weapons for information about missile lock.
Mechs can equip an Anti-Missile System (AMS) as an active defense to missiles. AMS damages missiles over time, so the longer the Mech has the missile in view the more missiles will be destroyed. Standard AMS uses ammunition and generates no heat, where Laser AMS does not use ammunition but generates heat.
Ballistic and missile weapons need ammunition to function on the battlefield. Ammunition may be stored in any location in whole or half-ton bins; both bin sizes take a single slot. The amount of ammunition per ton depends on the weapon system. During a match ammunition is expended in the following order:
Ammunition in the center torso is always used first, ammunition in the head is always used last; see the figure. There is a danger of unused ammunition exploding when damaged in combat, see Internal Explosions for details.