100cc attachment, the reflex sight slightly increases accuracy of the weapon, increases autoaim and autoaim snap when raised, moves the gun away from the sight so it doesn't cover up the lower part of the screen when aiming, and can be placed on all Assault Rifles, Light Machine Guns, Sub-Machine Guns and Shotguns, but not on a pistol, TMP or a sniper rifle.
Advice:
When in close combat, do not use the sight. It only slows you down.
If you are over the cc limit, remove the grip instead of the sight, the sight is far more important.
On a shotgun, it doesn't increase accuracy, but autoaim and autoaim snap are still there.
Recommended this be one of the first upgrades you get. The muzzle flash on most guns makes aiming without a sight like trying to shoot with flashbangs going off in your face every half a second.
