Weapon Mods are applied to assault rifles, shotguns, sniper rifles, submachine gun, and heavy pistolsto augment them in Mass Effect 3. Available mods include high-caliber barrels, scopes, and bayonet attachments, among others. Only two mods can be applied to a weapon at a time, and the same mod cannot be applied twice to a single weapon.
Once a weapon mod is found, it may be applied to any and all of the weapons of the applicable type at a weapon bench. Finding another instance of a mod the player already possesses will upgrade that mod to the next level. Likewise, shops will always carry mods one level above those the player currently has.
PAssault Rifle Upgrades
Assault Rifle Stability Damper
Distributes recoil with sliding system of counterweights compatible with kinetic coil generators. Reduces weapon kickback.
Changes the color of the weapon's handle and stock depending on level of mod.
Assault Rifle Magazine Upgrade
Increases magazine capacity, allowing more shots before reload.
Changes the color of the weapon's body depending on weapon and level of mod.
Small attachment to muzzle, causing massive damage to meleed targets.
Adds a visible stunner beneath the barrel. Also changes the color of the weapon's handle depending on level of mod. Adds electrical visual and sound effects to melee attacks that hit enemy with the gun.
Extended Barrel and High Caliber Barrel mod's damage bonus stacks additively with that provided by skills such as class or racial passives and powers. For example, an Infiltrator Shepard who took every weapon damage upgrade for Operational Mastery and Tactical Cloak and put a High Caliber Barrel V mod on his weapon will deal 100% + 10% + 90% + 25% = 225% of base damage.
Piercing and Shredder mods increase damage versus armored targets by ignoring part of damage reduction that every bullet striking an armored target suffers. A good approximation is to treat the result as a fixed (independent of weapon damage) damage bonus on every bullet (and every shotgun pellet) striking an armored target. As a result, rapid-fire weapons receive a much greater benefit from these mods than slow-firing ones.
High-Velocity Barrel mods: upon getting them to level 5 (V) for sniper rifles and shotguns, the extended barrel effectively becomes a weaker choice, since said mod only gives damage, as opposed to damage and pierce. Combined with a Piercing/Shredder mod, and a weapon with natural piercing abilities, one can penetrate unthinkably large amounts of cover and headshot enemies from as much as 3.7-4 metres.
The above method should however be circumvented on characters seeking faster recharge speeds for their powers as all High-Velocity Barrels add 50% weight onto the character.
Spare Thermal Clip ammunition mods tend to be more useful on weapons that have very little ammunition on reserve, such as the Reegar Carbine, or the M-98 Widow. While it is also helpful with weapons with a much larger reserve such as the M-13 Raptor, its effects are usually unnecessary unless playing against enemies on harder difficulties.
Extended Magazine Upgrade mods do not change the amount of spare ammo a weapon holds, however, the increased capacity is not deducted from the spare ammo pool either - if a weapon normally holds 100 rounds and 500 in reserve, applying a Magazine Upgrade V will change that to 180 rounds and 500 in reserve, for a total of 680.
Omni-Blade mods (and other mods that increase a character's melee damage) apply that melee damage bonus while holding a weapon attached with this mod; even if the character's powers and/or melee attack does not actually strike with the weapon attached with this mod. For example: the drell and krogan light melee, the gethand asari heavy melee, or the N7 Shadow's and N7 Paladin's light melee; even though these attacks will not trigger the sound and/or hit effects associated with the mod.
Optical/Thermal Scope mods (and other mods that increase a character's effectiveness at range): caution should be advised since these also decreases your peripheral vision. This can cause enemies to flank you more easily.