Overwatch Standard Issue Pulse Rifle

The Overwatch Standard Issue Pulse Rifle (OSIPR), often referred to simply as the Pulse Rifle, is a weapon manufactured by the Combine Empire, derived from modern human assault rifles for use by the Transhuman Arm of the Overwatch. It is fairly accurate at short and medium ranges and is best used in short, controlled bursts, since when firing continuously, it tends to wander due to the kickback. For added control, similar to assault rifles it descends from, it is equipped with a pistol grip.

As it's name suggests, the OSIPR is commonly issued to Overwatch Soldiers and Elites. The player first acquires the Pulse Rifle in Half-Life 2's sixth chapter, "We don't go to Ravenholm...", from a small group of Overwatch Soldiers who are fighting zombies on the train tracks near Shorepoint base. But you will first use the mounted Pulse Rifle in the Half-Life 2 chapter Route Kanal.

Construction
The rifle is manufactured from the same alloy most Combine technology is produced from, which guarantees durability and reliability in the field. The design is derived from modern human assault rifles, however, due to it's different working mechanism, it varies significantly. It's based on the Combine energy pulse technology, which in turn is derived from harnessing and controlling dark energy plasma; it's main advantage is that while bullets damage with kinetic energy only, dark energy plasma has extremely disruptive effects when contacting normal - especially organic - matter; simply put, hits will vaporize/cauterize flesh. The forward part of the weapon contains all the working mechanisms of the rifle - the magazine feed, the firing pin for the energy plugs, the energy barrel, the orb launcher and it's firing mechanism.

The barrel is additionally outfitted with a set of grips locking the plug in place.
 * The energy barrel is suspended over the orb launcher via a short metal beam, additionally fitted with an armor plate for protection. Inside, the energy barrel is laid with resistant material, which prevents the exploding energy from ripping the barrel apart and additionally helps direct the blast.
 * Magazine feed - the rifle utilizes special energy plugs, which are stored in Combine designed ammunition cartridges, resembling thin drum halves. Each drum is outfitted with it's own plug loading mechanism, as a measure to improve the weapon's reliability and minimize the amount of weapon's firing mechanism parts. The ammunition cartridges are mounted into the underside of the weapon and locked in place by a tiny mechanical pincer instead of the gunner's finger.
 * The firing pin - the firing pin, unlike human assault rifles, does not operate within the rifle's body, but instead operates outside of it. It is also significantly longer and larger than human pins, resembling a long spike. This design is required for it to effectively detonate the energy plugs.
 * The orb launcher is located directly underneath the energy barrel and in front of the plug cartridge. It is basically a tray outfitted with an OSI firing pin, large enough to detonate the charge and release the orb.

Working mechanism
The OSI Pulse Rifle posseses two fire modes: automatic energy pulse fire and orb launch.

This mode is fully automatic, and posseses a very high rate of fire, capable of discharging the whole plug in seconds. The lack of bullet casings to eject and the simplicity of design makes this a very reliable fire mode. Each loaded plug carries energy for thirty energy pulses.
 * Energy pulse fire (fig. 2a) - by pressing the trigger, the firing pin is released and hits the detonator of the energy plug. This action releases dark energy plasma stored within the plug. In normal conditions, it would burst outwards in all directions, but when it happens within the energy barrel, the energy is channeled and directed towards the end of the barrel at the unfortunate target.

Similiar to the primary fire mode, the mechanism required for this is very simple and reliable. Each charge carries a single energy orb.
 * Orb launch - this fire mode utilizes specially designed charges, containing inert Combine energy orbs. The charge is placed on the tray underneath the energy barrel, with it's detonator against the firing pin. When detonated, the forward part of the charge disperses into six parts (thanks to it's construction and the fins), releasing forwards an energy orb.

Design variations
Modified versions of the AR2 Pulse Rifle include the mounted AR2 heavy pulse machine gun, used in bunkers, on walls, barricades, and other positions suitable for placing the weapon.

The mounted AR2 heavy pulse machine gun has had the dark energy orb launcher removed, and the rate of fire amplified, to allow continuous suppressing fire. The barrel has also been redesigned, being enveloped in a red metal material to accommodate the increased heat caused by the increased firing rate while having the positive effect of increasing the shots range Surrounding the red material are three metal plates to protect the red material.

The mounted AR2 also uses a modified version of the standard AR2 pulse magazine, being much larger than the original. The weapon also comes with a mount which still allows the user to aim and move the weapon with ease. Because of the mounted AR2's increased firing rate and weight, the pistol grip found on the unmodified AR2 has been replaced with two handles, one containing the trigger.

The mounted AR2 has been used in numerous areas, mostly being used to defend positions. This is evident in Nova Prospekt, where watch towers would have mounted AR2 pulse machine guns manned by prison guards. The mounted AR2s are also seen with a searchlight for operation in poorly lit conditions.

Employment
The Overwatch Standard Issue, as it's name suggests, is primarily employed by the Transhuman Arm of the Combine Overwatch. It's versatility, accuracy and reliability make it an excellent choice for troopers operating often in hazardous conditions. It is also the exclusive weapon of the Combine Elite, who operate it with even deadlier skill than regular troopers. Additonally, only the Combine Elite are authorized for energy orb charges, since their employment requires high precision and proper training.

The heavy machinegun variant is used in entrenched positions and bunkers, as it provides extreme firepower in a very mobile and compact package. It's use is authorized for all branches of the Combine military, from Civil Protection to Combine Elite.

It is favored among members of the Resistance, who prefer it over the weaker SMG1.

Tactics
The OSIPR is an exceptionally powerful weapon if used correctly, but like every weapon in Half-Life 2, it has distinct advantages and disadvantages.

The easiest way is to simply treat it as a more powerful version of the SMG, which makes a great deal of sense, as the two weapons are very similar in function. However, the OSIPR has a number of differences from the SMG that players should take into consideration.


 * First, one must resist the urge to unload the weapon all at once, because it can only hold two spare clips of ammunition, which, combined with its high firing rate and poor accuracy while firing, cause it to tear through its ammunition like it tears through enemies. Fire in short bursts to conserve ammo.


 * Next, one should remember that the OSIPR's accuracy is, at best, below average. (Very poor by modern assault rifle standards.) This inherent inaccuracy is further exacerbated by firing the weapon fully automatic, so firing it in short bursts is highly recommended. Again, this also conserves ammo.


 * The cores that power the weapon's alternate fire are rather hard to come by. Conserve them, and when you have to use them, try to line up your enemies so that it goes through them all before it hits a wall, because having the ball to ricochet off a wall requires a bit of guesswork.


 * The cores are also known to be a one-hit-kill against even a Hunter. In enclosed areas, the ricochet can take out multiple hunters, saving ammo and health in the long run.


 * Remember the secondary fire has a short delay between the trigger and the shot actually firing. Keep the target lined up.


 * Note: the orb can not go through chain link fences, railings, or grates. it will just ricochet off. So don't try it. The orb will probably just bounce back and kill half of your squad.


 * Pay attention to what kind of enemies you're using the weapon against. Try to avoid using the OSIPR against antlions or zombies, because they do not carry ammunition for it, and you can only carry a few magazines at a time. Use it against Combine soldiers, as they are likely to have at least one OSIPR user in their squad from which you can source ammunition.


 * When using the heavy machine gun variation, due to the camera not automatically positioning you to the front of the gun, it is possible for you to operate it while behind cover, protecting you from most ranged attacks.


 * The reverse of this tactic also applies: you can knock energy orbs off course by using the Gravity Gun. Also, if you're inside the Citadel, don't hesitate to grab an Elite's freshly launched core and fling it back to the sender. Doing this will earn the "Think Fast!" achievement.


 * Exercise caution when combating Elites near deactivated Combine generators: a lucky shot from an energy orb can knock you into the generator and immediately reactivate it, resulting in instant death. The same applies to deactivated forcefields powered by generators.


 * Your best protection against OSIPR weapons is your suit energy. Your hitpoints will drop a lot more faster without any suit energy.

Trivia

 * The AR2 was originally going to be a OICW, but was changed.


 * The AR1 existed at one time and was supposed to be an AK-47.


 * The model of the AR2 is called the Irifle (v_irifle), which is the name of a cut weapon from the Half-Life 2 Beta.