A common misconception in Call of Duty is that one must lead his shots. This is not true. Even though one may assume that it takes time for your bullet to travel and then hit your target(like in the Halo series), this is not true. Once the trigger is pulled a bullet(hitscan) will hit the target with no delay. Any delay experienced in multiplayer is pure lag. Another note, ALL WEAPONS are completely 100% accurate. If you are on target and you shoot when your reticule(aimer) is on the target your shot, in theory, will 100% connect. The only reason that this may not seem to be the case is lag, or faulty hitboxes on the player models.
Each player will start out with 100 points of health. This health will recharge after 5 seconds, completely. hardcore mode has 30 points of health for a player. Health works by subracting the amount of damge you took until you hit zero, then you die. If a gun does 40 damage per bullet up close and 30 damage per bullet at a far range(like the Commando) it will take 3 shots to kill up close, and 4 at a distance. The only exception to this is headshots. Headshots offer a dammage multiplyer, meaning it does more damage to an enemy when you shoot them in the head. The damage multiplyer for the Commando for the head is 1.4 meaning a single shot up close(which is normally 40 damage) will now do 56(40x1.4). This means the Commando has the potential to kill in two shots if both shots are headshots.
I will continue into much more detail about game mechanics in future posts, thanks.