The pistol is your starting weapon, and your constant companion. At first glance, there is not a whole lot to be said about it. It fires slowly, does little damage and is generally inaccurate. You certainly don’t want to be using just your pistol in a pitched battle with an infected horde. There are, however, some advantages to using the pistol. For one, it never runs out of ammo. This means it can be useful for picking off lone infected or in other low-intensity situations, saving ammo on your primary weapon. It is also the only weapon you can use when knocked down, so make sure you get some practice with it. Finally, once you pick up your second pistol, the weapon becomes significantly more useful. You can use it in more situations, once comfortable with it, and save the ammo on your primary for more dangerous fights.
The Pump Shotgun and Auto Shotgun
The pump shotgun is one of two tier one weapons that you can pick at the beginning of any campaign. Despite being significantly weaker than its tier two counterpart, there is a lot of good to be said about this gun. It has a wide burst, meaning that you can take out multiple infected with it. At close range, it is deadly, and can save you from even a special infected if you aim correctly. The rate of fire is very slow, however, so it requires somewhat more tactical shooting than some of the other guns with larger clips. Slow, steady shots are required to make the best use of this gun, and it is best to leave distant infected to your teammates or your pistols.
The auto shotgun is the pump shotgun’s big brother. In terms of raw infected killing power, this gun is unparalleled. The pump shotgun’s slow pump action has been replaced with a much faster automatic reload and this allows you to fire your entire clip significantly faster. This can empty a room of infected if used intelligently. Be aware though, reloading the gun itself can take some time, so continue to use intelligent, tactical shots. As with the pump shotgun, the auto shotgun is devastating in close quarters, but even more crippled at range. Save your ammo for nearby enemies.
The SMG and Assault Rifle
The SMG is a less tactical weapon than the pump shotgun, but not much so. You can fire the entire clip in one long burst, sweeping it back and forth across the room, but this is rarely advisable. The gun is the most useful when used in short bursts - aim for the head, and you will get a huge number of kills per clip. This is very accurate at range if used in single shots or short bursts, so don’t be afraid to start firing from far away. Stay calm and resist the urge to spray and pray, and this gun will treat you well. In close combat, the SMG is still useful, but less so than the shotgun. Stand behind your allies with shotguns, or kneel and let them deal with the threat from behind.
The Assault Rifle is an extremely powerful weapon. A hit almost anywhere on an infected with this gun will kill or cripple them, so make good use of it. Even more so than the SMG, this gun is excellent at range, so take the time to pick off distant or isolated infected. What makes this weapon so fantastic is that it is powerful at close range too - with bursts or on full automatic, infected will have trouble closing with you as long as you have bullets to fire with. Be careful though, the spray on this weapon can get very wide, so make sure that your allies aren’t in range when you start to open up.
The Hunting Rifle
The hunting rifle is by far the most unique of the tier two weapons, and also the hardest to use. This weapon is the most powerful in the game, and its bullets can pass through walls, infected and most objects, making this a very tactical gun. It also has a scope, making it invaluable in large, open areas. Use this to pick off infected while they are too far away to retaliate and to scout out the next area. Shoot through walls where you suspect there are infected and use the increased accuracy to improve your headshot percentage. Be careful though, this gun is slow and can be inaccurate if you try and fire too quickly. It requires patience and skill, so rely on your teammates to deal with nearby threats while you thin the herd from far away.
The Molotov Cocktail and the Pipe Bomb
The molotov cocktail and the pipe bomb are your two options for your grenade slot, and you can only carry one, so choose carefully. They each have unique uses and drawbacks. The molotov cocktail explodes after you throw it, leaving a large patch of flame on the ground wherever it landed. Infected running through it will either be killed or slowed, making it ideal for using when in a choke point or back into a corner. Be warned though, hunters can use it to catch themselves on fire and do extra damage. It is also your first and best line of defense against a tank - one person on your team should always have one for defense against these brutes.
The pipe bomb is best used for crowd control. The beeping will draw all nearby infected to it and its explosion can kill dozens if it is thrown correctly. Use this when the horde is triggered, or to clear a particularly badly infected room. It has little use against special infected, so save it for when the team gets vomited on by a boomer or has to trigger a horde event.
The minigun is a mounted killing machine with a 180 degree range of fire and a devastating rate of fire. These only appear in specific places, but usually coincide with a horde event or a finale. Often, the places where these appear are not the most defensible, but if your team works together to defend the person on the minigun, it can make surviving a lot easier. Use it to sweep through hordes of infected, but don’t spare special infected if they wander into your range of fire - it can tear them apart in seconds. Use short bursts, because the gun can overheat, and make sure that your fellow survivors are watching your back, since you are a tempting target to sneaky hunters and smokers.
There you have it! Now you have everything you need to know about choosing the right weapon for the job in Left 4 Dead. Good luck and good hunting.