SAS: Zombie Assault 4
Rather than using a multiplying system, it simply adds the percentage of extra damage, default of +100% (basically twice damage) without Critical Shot skill. This is particularly powerful with high damage weapons, e.x. Hornet as it can destroy a boss or a tough zombie with much less effort, depending on crit chance and damage, than normal. Hitting a zombie with a critical the word 'Crit' displays in white text above the zombie for each shot (individual flechettes do not count unless they are from the 1887 Shockfield due to the actual projectiles being shot by the weapon). Critical hits do not affect damage over time, only the immediate damage. Critical hits are only available for gun shots, (and grenades as of December 10 2015 but this could be a bug.) not including turrets,and CQC Melee. Critical hits only apply on moving hostile enemies, not including zombie pods, hidden/breakable walls, zombie nests, and cars.
Critical Chance Sources
The standard chance for critical shots are 0% for all weapons. To add critical chance, the armor augmentation target assist adds a max of 7% crit chance, and for weapons, pinpoint adds a max of 12% chance. Generally, the most common source of crit chance is through the all-class skill crit shot, which adds a max of 16% crit chance and increases the crit damage bonus each level. The pre-mission power up Killing Machine adds 10% crit chance. Assuming you have killing machine purchased with full level 10 pinpoint & target assist, the max critical chance is 45%. Considering all you have to sacrifice for this (along with the money you will have to spend for the last 10%), this may not seem like a lot. However, considering that the crit shot skill increases the amount of extra damage that a crit does, this can be surprisingly powerful. However, since critical shot relies on regular default damage, adding certain % on the shot, augs such as pinpoint is not a smart choice even with full level Critical Shot skill.
Critical Damage Sources
Normally, a critical hit does double damage. However, with the crit shot skill, each point adds 4% extra damage for the crit, resulting in a max of +201% of normal damage per critical, slightly over triple damage. This makes the crit shot skill the base of most crit builds due to the massively increased damage for each crit. Critical hits stack with everything due to the fact that crit adds certain % ON to the non-crit damage.