The primary fire shoots a powerful bullet. Each shot consumes a fairly good amount of ammo. Headshots will do more damage than hitting other body parts. There is a medium-sized delay between each shots.
The alternate fire allows the user to look through the scope. The scope will make the screen grey-tinted, but provides a better crosshair than the default crosshair. The gun does more damage when fired while looking down the scope, to the point where it can kill most regular human enemies in one shot and kill stronger foes, like the Illuminati Elite Trooper, with two to three shots.
Always look down the scope before firing because of the damage bonus looking down the scope provides. This is particularly useful for headshots, as it can mean the difference between a target dying and surviving.
Because of how small the maps in IW are, it can be difficult using the scope. To get around this, point the crosshair near a target's head without looking down the scope, then quickly zoom in and see if the gun is pointing at the target's head. If it is, fire. If not, move the gun just a little bit until some part of the target's head is in the crosshair, then fire.
Scoped headshots can be used to take down the majority of foes in the game with little difficulty. The only foes that might give a sniper rifle user trouble are robots because of the reduced damage they take (except with the EMP converter mod), and monsters/transgenics, which are hard to land headshots on because of their size or constant movement.
Look for some cover before engaging enemies if possible. The delay between shots will make the player vulnerable, so being able to dart to cover while waiting for the chance to fire again will help the player avoid damage.
Try to keep a useful sidearm, like the shotgun or the Energy blade, handy for when enemies are very close. The sniper rifle is difficult to use when an enemy is very close to the player.
The Silencer is a must-have for stealthy lethal players. Being able to kill enemies without other enemies hearing the gun fire is very useful for picking off enemies one by one without them noticing.
For a weapon that can take down mechanical and human foes, install the EMP converter mod onto the gun. This will make sniper rifle shots far more powerful against robots than before, making it an effective weapon against them.
The large amount of ammo each shot consumes can be reduced with the Ammo scavenger mod, making it useful for those that plan to use the sniper rifle as their primary weapon.
A Refire rate mod will allow the user to fire faster, making it easier to take down groups of enemies.