Critical Hit

Overview
A critical hit is defined as damage to equipment that takes up critical space. This can cause that particular item to be destroyed before the section it is housed in is itself destroyed. A critical hit is equal in damage to the hit that scored the critical damage. It is only possible to deal critical damage to a area that is no longer protected by armor. Once the armor is removed, and internal structure begins to take damage, there is a chance that a critical hit can be achieved. When the internal structure does take damage though, that same damage might also be applied to one of the pieces of equipment installed there up to three times. The odds for a particular piece of equipment taking a critical hit depends on how many critical spaces it takes up and how much critical space is occupied by other pieces of equipment.

Notification of Critical Damage
When your 'Mech takes critical damage, you will see a large warning on your screen like this one:

Knowing when you deal a critical hit requires closer attention. If you manage to destroy an enemies ammunition bin, you may see a secondary explosion come from within the section after you damaged it. In this case, further damage will be dealt to the location it is housed in and possibly to the adjacent section.

If you destroy an enemies weapon, you might see the weapon displayed in red on your HUD even though the section it is housed in is still intact.

Odds of taking/dealing a critical hit
Most weapons have a less than even chance of dealing critical damage. In most cases, damage that is dealt to internal structure has a 42% chance of dealing additional critical damage.
 * Each hit to the internal structure for most weapons have the odds of doing the following amounts of damage:
 * A 25% chance of the damage also causing 1 critical hit.
 * A 14% chance of the damage also causing 2 critical hits.
 * A 3% chance of the damage also causing 3 critical hits.

Since each critical hit is equal to the hit that achieve the critical damage, it is possible to magnify the damage of your weapon many times over.

Some weapons have a much greater chance of achieving a critical hit. Machine Guns, Flamers, and LB 10-X Autocannons have a 2 in 3 chance of dealing at least one critical hit.
 * Each hit by these weapons to the internal structure has the odds of doing the following amounts of damage:
 * A 39% chance of damage also causing 1 critical hit.
 * A 22% chance of damage also causing 2 critical hits.
 * A 6% chance of damage also causing 3 critical hits.

Odds of a specific item being hit
Assuming a critical is going to be dealt to a section, the odds of a particular item being hit depends on how many critical spaces it occupies and how many other spaces are also being occupied.

For example, there are 12 critical spaces in a side torso. Placing an LB 10-X AC (which occupies 6 critical spaces) with six single heat sinks (each occupies 1 critical space) will fill that section with equipment. The odds of the Autocannon taking the hit is 50% since it occupies half the total occupied critical spaces. If the section house the Autocannon and only three single heat sinks, there would be a 66% chance for the Autocannon to take the critical hit since it occupies 6/9 of the total occupied spaces.

Weapons can deal critical damage up to three times. Which equipment takes the critical hit is randomly determined per each critical based on their size and number of occupied critical spaces.

Crit Buffing
Adding expendable items to a section that is occupied by a more important item is an effective way of decreasing the odds of the important item taking a critical hit. Popular choices for crit buffing are Heat Sinks and Gauss Rifle ammo (the only ammo that does not explode). Critical spaces occupied by Endo-Steel Structure and Ferro Fibrous Armor do not count towards the number of occupied spaces. Actuators, engines, and gyros also count towards the number of occupied spaces but none of them can be destroyed by critical hits. That might change in the future though.

Calculating the Damage
Most weapons will deal the same amount of damage they do to the internal structure as they do for each critical hit. For example, if an Autocannon 10 hit internal structure and achieves 2 critical hits, it will deal two separate critical hits of 10 points to internal equipment.

The exception are the critical seeking weapons like the Machine Guns, Flamers, and LB X Autocannons.
 * Flamers will deal 110% damage (0.77 damage) to internal components
 * Machine Guns will deal 1,350% damage (1.08 damage) per bullet
 * LB X Autocannons will deal 200% damage (2 damage) per pellet

Ammunition/Gauss Rifle Explosions
When an ammunition bin is destroyed by a critical hit, it has a 10% chance of detonating its remaining ammunition as an internal explosion. When a Gauss Rifle is destroyed, it has a 90% chance of exploding, and dealing 20pts of damage to the section it's housed in. When a section housing either ammunition or a Gauss Rifle is destroyed, each ammunition bin and rifle has a 10 or 90% chance of exploding respectively.

With the above info in mind, one must be careful where they place ammo in their 'Mech. An unlucky ammo explosion in a leg could spell doom for a light chassis. On the flip side, an ammo explosion in the side torso might travel to the center torso, and destroy the engine. The Gauss Rifle is a particularly hazardous weapon to field, due to its low health (5pts), its high chance of explosion on destruction (90%), and its large size (7 critical spaces). These risks can be mitigated with a CASE.

Guide
Read Crits And You - A Brief Guide for addition information and suggestions on critical damage.