Battlefield 3 offers a vast selection of attachments for most weapons ranging from sights to suppressors. Each attachment can be unlocked by playing with the specific weapon over time. Below is a full list and explanation of weapon attachments offered in Battlefield 3. Unlock progressions can be found here: Battlefield 3: All Weapon Unlocks by Class
The ACOG 4X zoom is often the first attachment unlocked for assault rifles. It’s a 4X zoom sight that doesn’t reflect or glare, thereby doesn’t give away your position to the enemy.
Ballistic sight, 12X
The Ballistic sight offers a powerful 12X magnification and is best suited for sniper rifles. However, enemies can easily spot you due to its powerful glint.
The Reflex RDS sight offers no zoom but is very useful in tight quarters where precision and reaction times are important.
IRNV Infrared sight
The IRNV Infrared sight brings infrared capabilities, making it easy to pick out enemies from the environment. It has a 1X zoom.
The Russian-made PKS-07 comes with 7X zoom and is the standard scope op Russian-made sniper rifles.
The M145 has a slightly less powerful zoom (3.4X) than the ACOG 4X, but offers better visibility and is better suited for in-door combat.
The PSO-1 is the Russian answer to the ACOG 4X, and works in much the same way, offering the same zoom and aiming capabilities.
HOLO Holographic sight
The HOLO is the main holographic sight for the US forces.
The PKA-S is the Russian answer to the American HOLO sight, and works in much the same way.
The KOBRA RDS is the Russian answer to the American Reflex RDS sight, and is nearly identical in its function, although its appearance is quite different.
The PK-A is the Russian counterpart to the M145, and offers the same zoom and features.
Under barrel attachments
The foregrip increases accuracy by decreasing horizontal spray when used on assault rifles and sniper rifles.
M320 Grenade launcher
The M320 grenade launcher is unlocked for assault rifles and can be used with a frag round, shotgun round, or smoke round.
The bipod is available for assault rifles, sniper rifles and light machine guns and. When mounted on a surface, it greatly reduces recoil and increases accuracy.
The tactical light is a powerful flashlight which can be attached to all weapons, including pistols. Other than making it possible to see in the dark, the flashlight can be used to blind opponents as well.
The laser sight emits a powerful laser which is useful and increases accuracy when firing the weapon from the hip / unscoped. however, the laser also easily gives away your position.
The heavy barrel, available for assault rifles, increases long-distance accuracy, but the trade off is that it’s less usability in close ranges.
The suppressor is available on most rifles and sniper rifles, reduces the noise and removes the muzzle flash when equipped. However, it also deals less damage at all ranges.
Unlike the regular suppressor, the flash suppressor doesn’t dampen the noise, but it greatly reduces the flash weapons give off, while still retaining the same damage inflicted to opponents.
The extended magazine is available so SMGs (sub machine guns) and offers a larger magazine holding more ammunition per clip.