Called the Javelin by Alliance marines, this geth weapon holds a reservoir of ferrofluid, magnetically drawn into the firing chamber and expelled at lethal speeds. Like a high-pressure water-jet, the ferrofluid cuts through nearly anything it hits with so much heat that it resembles a beam of light, causing terrible wounds.
It has a native 100cm penetration rate, which is enough to pierce most thin cover.
With the Sniper Rifle Piercing Mod added to the Javelin, the penetration distance gets even larger, but won't increase the damage done to enemies after penetrating through cover/objects.
The Javelin's innate thermal scope will allow players to see through as much cover as it can pierce. This feature scales with weapon mods that increase its piercing ability.
The combined penetration of the 1.10m from the Sniper Rifle High Velocity Barrel's + 1.35m from the Piercing mod + 1.00m from Javelin's = 3.45m. Drill rounds III provides an additional 2.5m of penetration, for a grand total of 5.95 metres: allowing players to both see and pierce through almost (if not) everything: even multiple walls.
There is a short charge time for the weapon before it fires, which could compromise moving shots. This "lag time" between pull and shot can actually benefit the shooter if the target moves unexpectedly, allowing the user a split second to realign the shot before it goes off.
There is a slight problem with the Javelin and its "lag time": Since the Javelin is a charge-up weapon, if you suddenly take your finger off the trigger and decide the shot is not worth it, you will still break your Tactical Cloak. This forces you to take the shot if you put your finger on the trigger and can cause you to miss shots, or if you are lucky, get a shot off and kill a different target.
In single-player, the Javelin deals roughly the same damage as the M-98 Widow, however in multiplayer it deals about 20% more damage, thus placing the Javelin as the most powerful single-shot weapon in the game, Claymore aside.
The Javelin is a very powerful piercing weapon, starting off with its own natural high piercing thickness and high damage when piercing, and when paired with the piercing mod the Javelin can even pierce thin walls to pick off enemies with headshots.
In multiplayer, a Geth Soldier, Engineer or Infiltrator with the rank 6 "Sniper and Assault Rifles" evolution of the Networked AI power reduces the weight of any and all sniper rifles and assault rifles equipped. The Javelin and Geth Pulse Rifle pair well with each other.
Level-one Networked AI also allows the player to deal 2.5% weapon damage and 5% more damage with Geth weaponry which include the Geth Spitfire, Geth Pulse Rifle, Geth Javelin, Geth Plasma Shotgun and Geth Plasma SMG. If you choose the "Weapon Damage" perk instead of the "Sniper and Assault Rifles" evolution mentioned above, you can deal 12.5% more damage with every weapon and an additional 10% with geth weaponry.
The Geth Infiltrator can also pick up additional damage and sniper rifle damage while cloaked. Add this to the damage bonus from Hunter Mode, and the above-mentioned damage bonuses from Networked AI, and your damage bonus can be over 180%.
For the Geth Engineer, you can combine the Javelin for longer range encounters, and a shorter range weapon, like the Geth Plasma Shotgun, if you focus only on Hunter Mode and the Geth Turret, since neither of those require quick cooldown times.
When reloading, if the reload is cancelled at the right time, you can reduce the time it takes by half.
With the highest-level piercing mod, the Javelin is able to shoot through almost any cover, including thick walls and floors. This is most observable in multiplayer, where the battlefields are on different levels and many different locales are present. A level V piercing mod allows the Javelin to hit enemies through the floor of array control on Dagger.
The Javelin is about 20% heavier than the Widow and the Claymore. An update on June 26 has lightened lower levels of it slightly. However, since it does not change the weight at level X, it does not do much in curing the weight problem.
The Javelin is perhaps the most challenging sniper rifle to use effectively in multiplayer. The lag time between pulling the trigger and firing the shot takes some getting used to, and can make hitting a moving target very difficult at first. Even those experienced with the Javelin in single player may find it frustrating, since in multiplayer there is no way to slow down time when aiming. However, with practice, the Javelin can become an absolutely devastating weapon in the hands of a skilled marksman.
The need to be precise with this weapon is even higher than other sniper rifles since the lag time can be confusing and can cause you to miss due to you needing to maintain the target for a good half second upon firing. With a slow reload and only a single shot before needing a reload, this may quickly spell death on most difficulties. For this reason Tactical Cloak may help to alleviate some pressure from you unless you are the last man (or woman) standing. Because the weapon is heavier than any other, one may as well take another heavy weapon to ensure they are adequately equipped to deal with any situation should the enemy draw in. Be wary though, when you cloak the foe may notice you cloaking and may still be able to kill you as a result. Be warned that fast moving enemies like Phantoms or Dragoons can cause no end of grief if you stick to using just the Javelin, so it would be recommended to equip a shotgun, or strong close quarters backup weapon to assist you.