The Raptor is a human version of a turian weapon developed for conflict on the low-gravity world Amar. Fighting at longer ranges than expected, the turians optimized a low-recoil, semi-automatic rifle with a scope, and issued it to their regular infantry, creating a hybrid weapon that was half-assault rifle and half-sniper weapon. Cerberus assigns the Raptor to Nemesis snipers.
Functionally similar to semi-automatic assault rifles, the Raptor offers a higher rate of fire and comparable accuracy at the cost of a slight increase in weight and lower damage over the M-96 Mattock when fully upgraded. However, because it is classified as a sniper rifle, it has a built in scope which allows an upgrade slot to be freed up instead of being used for an Assault Rifle Scope when compared with the Mattock. This means you could go into battle carrying the equivalent of two assault rifles, meaning you could have the power of a semi-automatic rifle and still have a fully automatic weapon without having to use a weaker SMG.
The Raptor weighs the same as the Mantis, thus it is fairly heavy until upgraded.
The Raptor can be reloaded very quickly, in a similar fashion to the Viper and Valiant. Like the two mentioned weapons, if reload cancelled correctly, reloading is nearly instantaneous, effectively allowing for an almost constant rate of fire. This, of course, is at the expense of faster ammo consumption.
The Raptor can be used fairly effectively with ammo powers, especially cryo ammunition, where it can freeze several targets in a short space of time. While it's not as effective as area of effect weapons like the M-37 Falcon, or the Striker Assault Rifle, it has accuracy and a very quick reload, and doesn't stop firing for rate of fire issues.
An Infiltrator can use their cloaking abilities to inflict incredible damage. The ability to "spam" the trigger on the Raptor can allow an Infiltrator to fire off up to 20 shots (with a perfect reload cancel) with the 125% extra damage output, or higher when combined with damage increasing powers such as Hunter Mode. This can easily take out large groups of small infantry, especially when the Piercing and Barrel mods are attached, which make it even more effective at killing enemies. These mods also allow the Raptor to bypass the Guardians shields or plating on Reapers and increase damage to bigger enemies.
The Targeting VI will prove to be a tremendous boost to the Raptor, especially over higher damage sniper rifles given the lack of waste damage produced, as the +100% damage on headshots will boost it to the level of a one, or two headshot gun on most humanoid foes. This makes the Raptor jump from simply being a good damage per second gun to being a versatile gun that will clean up standard foot soldiers with alarming speed even on gold difficulty. While the Incisor can also gain this benefit due to it also having a 15 round clip and the same damage, its burst fire nature makes it much more difficult to land consecutive headshots as opposed to the Raptor. Combining the Targeting VI with disruptor ammo, the Raptor becomes capable of shredding almost any target with brutal efficiency and speed.