No kills: 10% or 1/10
- 20% or 1/5
- 30% or 3/10
- 40% or 2/5
- 50% or 1/2; the chances of extra damage remain at 50% past a 4 killstreak.
It should be noted that the percent chance of doing extra damage with a shot is probabilistic and not set in stone for any particular shot. For example, a player on a 4 or longer killstreak (50% chance of extra damage) would, out of a magazine size of 30 rounds, theoretically have 15 of those shots do 40% more damage. However, it may work out that more or less rounds have the effect applied. A similar analog would be flipping a coin a set amount of times, which represents firing a shot, and counting the number of heads, which would represent a +40% damage hit. This is the same case with the other chances of getting a higher damage shot but with different probabilities. 
This perk is best used on guns with damage that would see a decrease in Bullets To Kill (BTK) from the likely amount of damage increases. The weapons that receive the most benefit from this effect are those that do 42 to 49 (50 or higher is a two hit kill regardless of the perk) damage at their maximum effectiveness. This way, only one out of two theoretical hits would need to receive +40% damage for a two hit kill to be achieved. This is because 42 x 1.4 = 58 for a Deadeye hit, and 42 added on to this for a non-Deadeye hit would still be more than 100. By this math, weapons such as the ARX-160, AK-12, and Remington R5 are excellent choices because they will all benefit from this perk greatly, as they deal a maximum of 43, 49, and 49 damage respectively. On the contrary, a weapon such as the MTAR-X, with a maximum damage of 40, will only be a two shot kill if both of two theoretical hits are Deadeye hits; this is because the damage of a Deadeye hit, 56, plus a normal hit, 40, only equals 96.
It affects Shotgun damage per pellet. Although the red hit indicator may not show up sometimes when using a shotgun with Deadeye, it is still likely that the shot was affected by the perk. Using deadeye with a shotgun will increase one-shot kill range, so long as slugs aren't used, due to the higher damage in some pellets,
This perk is best used in a loadout where the player uses only a Primary weapon and the Specialist Strike Package, since it takes up almost half of the Perk Points available and it would be difficult to slot in any other wanted perks if the player does not use Specialist. Because of the way the Specialist Strike Package works in Ghosts it is highly recommended to use Deadeye in the equipped perks rather than have it be earned via pointstreak, as even setting it as the first perk earned would require 6 points (each perk requires its perk point value +1 to earn).
- Deadeye has the highest value of allotted perk points in Call of Duty: Ghosts at 5, the highest Squad Points price to unlock at 15, and is the last perk to be unlocked via ranking up at level 60.
- ↑ 
- ↑ https://docs.google.com/spreadsheet/ccc?key=0Ak5jPL93BMpldHdGX2E2dWpTX19PNVJfWS1IX1BoUnc&usp=drive_web#gid=8