Alien Swarm/Weapon one and Weapon two

Alien Swarm is rife with various tools, weapons, and miscellaneous items that can help you destroy the Swarm, heal your allies, or a myriad of other special effects.

Upon selecting a campaign to play, players are prompted to select both their character and a choice of two primary weapons, as well as a single secondary weapon. The two primary weapons can be changed at will; the secondary item is used by pressing the 1 key.

Aside from the left mouse button, which uses the default fire mode (for example, the standard assault rifle simply shoots bullets), it is possible to click in with the mouse wheel to execute the weapon's alternate firing mode, assuming it has one (for the above example, the assault rifle would fire a grenade which detonates on impact with a target or the ground). Right-clicking allows players to execute a melee combo attack which is effective against enemies too close for enemy fire. Much like other Steam games, friendly fire cannot be disabled, and on higher difficulties can be the bane of players. Using the melee prevents friendly fire.

When a reload order is issued, either through running out of ammunition in your given clip or manually (R by default), a small gauge appears at the centre of the screen. Hitting R when the cursor is over the white highlighted section of the bar will prompt the character to perform the reload far faster than usual. It is accompanied by a white flash on the weapon's muzzle and possibly a character quote. Failing to hit the reload button at the right time causes the weapon to jam and become unusable for a longer period of time. Avoiding the reload button entirely performs a standard reload. This fast reloading method is necessary to obtain the Quick Reload and Gunslinger achievements.

Players can carry two primary weapons and a single secondary item at any given time. It is possible to exchange these items, or press G to drop a given primary weapon. This is most useful if it is out of ammunition.

22A3-1 Assault Rifle
Standard issue assault rifle available right off the bat. Rounds don't do much damage, but is offset with its decent rate of fire. Secondary fire mode fires the attached grenade launcher and is one of the few explosive ordnance available for low levelled players. Best used against drones while still lending a hand at taking down larger targets. A versatile weapon useful throughout the whole campaign.

22A7-Z Prototype Assault Rifle (Technician)
A rifle useable only for tech marines. Primary fire functions identical to standard issue assault rifles, but with added auto aim. Instead of frag grenades for its secondary fire, it fires stun grenades. Useful for getting yourself or a teammate out of a pinch without the punishing friendly fire.

S23A SynTek Autogun
The SynTek Autogun is a hi-tech squad automatic weapon of the Alien Swarm universe. Similar to the M56 Smart Gun found Aliens versus Predator, it's large magazine allows for sustained fire and it features a target tracking device that offers auto aiming for multiple targets. However, its weight slows the user down and it is only available to Special Weapons class. While its modest rate of fire makes it quite capable at handling all but the largest swarm attacks, it is not as efficient at taking out larger swarm creatures. Best used at medium to long range to make full use of its auto aiming capabilities.

M42 Vindicator
The Vindicator is the first shotgun available in the game, but it is restricted to the Officer class only. That said, however, the Vindicator is the ideal combat shotgun, boasting a far higher rate of fire and magazine size than the standard-issue version. It also sports incendiary grenades which can let it replace the flamethrower in some circumstances. Overall, the Vindicator is a highly effective and deadly weapon, effective at short and medium range.

Official Description: The M42 Vindicator is a pneumatic assisted pump-action shotgun with a dual, selective magazine system. IAF standard ammunition loadout provides for 12-gauge rounds in one magazine and a number of timed incendiary grenades in the other. The Vindicator is only issued to NCO rank marines.

M73 Twin Pistols
Two handguns used together. Each shot from a handgun does more damage than those fired from the standard assault rifle but the handguns can only carry a total of 24 rounds, meaning more time spent being vulnerable while reloading. The twin pistols is the only weapon that can be fired without movement speed penalty. All other weapons available will cause the user to lose speed when they fire. A good aim and being able to fast reload consistently is required to make the most of twin pistols.

Model 35 Pump-action Shotgun
A very powerful shotgun available for all classes to use. Does more damage than the vindicator, it can take out large swarm creatures with a few solid hits. Unfortunately, it is hampered with its small magazine size and the maximum amount of total ammunition carried. Nevertheless, it is still one of the most powerful weapons available for low levelled marines.

IAF Tesla Cannon
The Tesla Cannon is a weapon that shoots out short-ranged bolts of electricity that stuns and slows swarm creatures, rendering them ineffective. It does very little damage, so it is best utilised as a support weapon for its slowing effect. The bolts are capable of jumping across to other nearby enemies. This makes it capable of slowing down swarm creatures that attack in groups such as drones, buzzers and parasites. Can also stun large swarm creatures, making them easier for your squadmates to take down.

Precision Rail Rifle
Firing projectiles at super high velocities, the Rail Rifle fires powerful shots that can penetrate all targets in its path. Must be reloaded with every shot, its best used on large swarm creatures at a distance. A difficult weapon to master, it is the only long ranged damage weapon option available until the Marksman Rifle is unlocked later on.

IAF Medical Gun
A piece of equipment that medics can use instead of the healing beacon. Aim it at a injured marine and it heals them. You can also heal yourself with alt fire. Good to heal while keeping the squad moving, but can only heal one marine at a time. The medical gun cannot be reload and is discarded once it is expended.

K80 Personal Defense Weapon
Two submachineguns that can dish out large amounts of damage at a high rate of fire through the simple expedient of wielding both of them at once. Lacks versatility and ammunition can be quickly depleted on big levels if used as a primary weapon. Carry ammo satchels or carry an extra pair for aditional magazines.

M868 Flamer Unit
A weapon that shoots out gouts of fire, causing targets to burn and take damage over time. With only short range and low initial damage, its well suited for taking out drones. The burning causes them to slow and recoil slightly and the flames can pass through and ignite other targets. Secondary fire uses a fire extinguisher, incase you set your teammates on fire and to get pass fire hazards present on certain levels. Although its low damage restricts its usefulness against stronger targets, it can burn away biomass to open up blocked passages.

IAF Minigun
The Minigun does the same amount of damage as the autogun, but its rate of fire is greatly increased. While it may not have auto targeting like the autogun, it can deliver a hail of fire that can overcome even the most concentrated drone attacks, and quickly take down large swarm creatures. However, the wide spread of fire means you have to get close to large swarm creatures for all shots to hit and its lack of auto aim and high rate of fire means your ammunition being quickly depleted. The gun requires a spin up, making you vulnerable to surprise drone attacks and being overkill for taking out one or two drones. This weapon is best used when playing on insane difficulty where drone attacks are large and numerous.

AVK-36 Marksman Rifle
Not as powerful as the rail rifle, but easier to use because it doesn't require constant reloading after every shot. Secondary fire brings up a scoped sight that uncovers darkened areas and highlight enemies. The damage tradeoff for versatility against lesser swarm creatures makes the Marksman Rifle favored over the Rail Rifle for some marines.

Chainsaw
A tool made for cutting used as a melee weapon. Its high damage causes lesser swarm creatures to explode upon contact with its spinning teeth. Can be used indefinitely without reloading, it also benefits from the bonus melee damage some marines have. While it might kill drones on contact, using it while retreating will make drones lunge at you, and large drone swarms can flank and overwhelm you. Many people will used the chainsaw as a weapon of last resort, certain situations will favor the chainsaw in holding back the swarm while conserving ammunition.