Percentages after # of kills 
No kills: 12.50% or 1/8
- 16.67% or 1/6
- 33.3% or 1/3
- 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 5 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 with lower damage weapons because they will gain the greatest benefit from the occasional damage increase. Higher damage weapons, such as Sniper Rifles, Marksman Rifles, and other more powerful guns such as the MSBS already have a high base damage output and would not be benefited greatly from the use of Deadeye except at very long ranges. Low damage Assault Rifles (ARX-160, SC-2010, FAD) Submachine Guns (CBJ-MS, Vepr, K7), and Pistols (.44 Magnum has probabilities of one-shot-kills) are good choices because a number of them will occasionally be granted two shot kills at close range and have their times to kill over longer ranges decreased when the perk effect is applied.
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.
This perk is best used in a loadout where the player uses only a Primary weapon and the Specialist Package, since it takes up almost half of the Perk Points a player has available, and it would be difficult to slot in any other wanted perks if the player does not use the Specialist Package.
- 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.