Pistol

The M1911A1 pistol is the backup weapon of all survivors. It is also the only weapon they can use when knocked down, although with a slower rate of fire and greatly decreased accuracy. Besides the minigun, the pistol(s) is the only weapon that has infinite ammunition. However, they are still limited to a magazine capacity of 15 rounds.

Even though they are meant as emergency weapons, the pistols make great secondaries, or even primaries for hunting rifle and shotgun users. They pack a punch slightly greater than that of the assault rifle, and possess above average accuracy.

Dual-wielding
If a second pistol is found, they can be dual-wielded. Second pistols are placed periodically from the Director, and can also be picked up from fallen teammates. This allows for twice the ammo capacity, as well as the rate of fire being increased from 300 RPM to 600 RPM. The downside of having two pistols is that it takes slightly longer to reload, but the extra damage and rounds are worth it. When dual-wielded, the pistol in the left hand will not have a light.

Left 4 Dead 2
In Left 4 Dead 2 there appears to be another pistol installed for the survivors, the HK .45. It is unknown if the pistol is stronger or faster than the M1911 that still remains in the game.

In one of the footage videos of the Left 4 Dead 2 beta it has been seen that one of the pistols fires as an automatic weapon. It is unknown if it is the submachine gun that has the full-auto capability or a pistol.

Tactics

 * Pistols can be quite effective in the right hands. However, to be an effective pistol user, you must be accurate; try to crouch when the situation permits, as it will tighten your crosshairs and accuracy.
 * The pistols have great accuracy, and a pistol user must take advantage of this. When using a pump shotgun or auto shotgun, it is a good idea to use pistols for distant targets.
 * When using the hunting rifle, it is advantageous to use pistols while running.
 * In certain situations, switching to pistols may be a better option than waiting for your reload.
 * If a distant teammate is disabled by a Hunter or a Smoker and your magazine is empty, then draw your pistols and open fire. This will probably kill the boss Infected faster than if you were to reload, reducing the damage taken by your teammate.
 * Pistols have unlimited ammo, so switching to them will conserve your primary ammo for more dangerous situations, such as a Horde or Tank.
 * The faster you click the mouse/press the trigger to fire, the faster the pistol fires. However, it's not automatic, so holding the button down does nothing.
 * Like any other weapon, try to keep your pistols fully loaded even when you're not using them.

Trivia

 * The pistol is produced by the fictional company "Finleyville Armory." The name is derived from the Pennsylvania borough of Finleyville and may be meant to sound like Springfield Armory, a manufacturer of several kinds of popular 1911 pistols.
 * On closer inspection, the Pistol seems to resemble either Springfield Armory Mil-Spec/Auto-Ordnance M1911 models, perhaps an early model were featured in-game. It has slanted slide cocking serrations, as opposed to straight ones from the original M1911. It's also fitted with what seems to be Sure-fire pistol lights. It looks to combine features from both Springfield Armory Mil-Spec and Auto-Ordnance.
 * An actual single stack 1911 (which is what the in game model is based off of) uses 7, 8 or 10 round magazines. There are 1911s that hold up to 14 rounds, but they are built on double stack (where the rounds are staggered to increase capacity) frames and are quite bulky. In fact, they are more often used for competition and range shooting than actual use.
 * The set-up of the 1911 in Left 4 Dead is somewhat odd: It uses stainless steel components and a fairly modern frame, with a beavertail grip safety, extended thumb safety, rounded hammer and integral light rail, but has 1911A1 style sights. The original 1911A1 stock sights are much harder to use than modern 3 dot sights, or even blade, and are almost never used on modern 1911s.
 * There is a glitch that can be performed when a Survivor has been downed and is only able to use his/her pistol. While shooting at Infected (or teammates, whatever you're into) you can hold the melee key (left trigger for Xbox 360 users) to silence your pistol. It doesn't change the damage caused the weapon, and Infected seem to react the same whether or not you use it. It's more or less just something cool to show your friends while you're down.
 * Players can receive the Akimbo Assassin achievement by completing a campaign using only the pistol (or pistols) as firearms.
 * You can: (all of these are fine)
 * Fire pistol(s)
 * Pick up a Gas can, a Oxygen tank, or a Propane tank
 * Melee with anything
 * Heal with Pills or a Health kit
 * Be healed
 * Throw a Molotov or pipe bomb
 * You shouldn't: (all of these might make you lose the achievement indirectly)
 * Pick up Tier 1 weapons, Tier 2 weapons or mount a minigun (picking it up/mounting it means a fellow survivor cannot take it. Plus, if you make one mistake, you will lose the achievement.)
 * Go "Idle" when attempting this achievement. If the AI controls your player, they will most likely pick up any better weapon they find, and use it if you are idle long enough.
 * You can't: (all of these WILL make you lose the achievement immediately.)
 * Fire a Tier 1 weapon, Tier 2 weapon, or a minigun.
 * Not play an entire campaign (not getting rescued or not starting at chapter 1)
 * Also, you may need to play the campaign on an easier difficulty or have a few practice rounds.