Auto Shotgun

"Those bastards think they're sick now, wait'll they get a taste of this."

- Francis

"Oh hell yeah, I'm takin' an auto shotgun."

- Coach

The Tactical Shotgun (formerly Auto Shotgun in Left 4 Dead) is a Tier 2 weapon and is a more powerful version of the Pump and Chrome Shotgun that does not require a pump after each shot. It also has a slightly higher DPS than the Combat Shotgun at point-blank. It holds a maximum of 10 shells at a time with 90 in reserve in Left 4 Dead 2. It is the best short-range weapon in the game, capable of firing extremely fast and taking out massive numbers of Infected per shot.

Both shotguns allow topping off the magazine on the fly, and the reloading process can be stopped to handle sudden threats. However, in Left 4 Dead if you are reloading when empty, you will cycle a shell into the chamber at the end of the reload, regardless of whether it was finished or interrupted; in other words, if you try to shoot after you loaded the first shell in the empty magazine, first you'll see the pumping animation only after which you can shoot. A good trick is to interrupt a dry reload after the first shell is loaded by clicking the fire button, because the following reloading process will proceed faster (in addition to that, this way you'll be able to fire the weapon any moment in case a threat appears). Another tip is just to reload constantly and always keep at least one shell loaded.

The relatively low capacity, low accuracy, and short range compared to other Tier 2 weapons make it slightly less effective against Special Infected. Its high damage output does allow it to wound a Special Infected seriously, but only at a dangerously close range. The exception to this is against Tanks, where the scatter of the shotgun is virtually all offset by the massive target a Tank presents. However, due to the damage penalty the Auto Shotgun has against Tanks, the Assault Rifle is preferable for them. Its rate of fire can be increased by quickly pressing the button instead of holding it down. It is generally a good idea to have at least one member of the team use a shotgun. Like the Pump Shotgun, it can kill a Witch with one hit if fired into her head while she is not attacking, making it useful for getting the "Cr0wnd" achievement.

The Tactical Shotgun is used by Coach, Francis (L4D only) and Louis (L4D2 only)

Pros

 * The Auto Shotgun is excellent against hordes of enemies, especially in tight areas like houses or hallways, because they can take out several enemies in a few good shots.
 * It has good penetration against the Infected. This combined with their spread makes it a powerhouse against a Horde.
 * It will normally kill Infected in one hit (if close enough).
 * Very effective against Special Infected at close range.
 * If a Witch is getting close, an Auto Shotgun is the best weapon for killing her before she can deal damage.
 * Can easily cr0wn a Witch.
 * It is reloaded with individual shells, so reloading early results in a very quick reload.
 * It is very, very effective against the Tank, despite the special damage penalty against it, especially when the holder has Incendiary Ammunition or Explosive Ammunition, or if the entire team is equipped with them.
 * One full magazine at point-blank range (which can be fired in as low as 3 seconds) is enough to kill a Tank on Easy difficulty, even taking the 15% or 25% damage penalty into account. Normal requires two, Versus requires three, and Advanced and Expert require four. Theoretically, if all four Survivors use automatic shotguns and fire at point blank range, it is possible to kill a Tank on any difficulty in 3 seconds or less.
 * Pairs well with Pistols or a Magnum for long-range targets
 * The gun can be partially reloaded; if a reload is started and subsequently interrupted, the gun is not left with zero ammo, unlike guns that use magazines.
 * Reloads can be interrupted manually to maintain safety while still refilling the magazine.

Cons

 * Wide spread (4.0 x 8.5) deems more ammo consumption while dealing with mid range threat.
 * If you're surrounded or in a wide-open area and facing a Horde, this is not a good weapon, as you have to reload often and can't take out many enemies at once if they're scattered.
 * Due to the high rate of fire and ammo capacity of 90 shells (in Left 4 Dead 2), the Auto Shotgun burns through ammo quickly if fired continually, and this may become an issue on higher difficulties if ammo conservation is not taken into account.
 * It can only hold 10 shells at a time, giving it the lowest capacity of the Tier 2 weapons, along with the Combat Shotgun.
 * This and the Pump Shotgun are the worst long-range weapons, as the lead shot scatters. It is not recommended to attempt to pick off distant Infected with this gun, especially Special Infected.
 * If the magazine is empty or nearly empty, it has the longest reload time of any weapon.
 * With automatic weapons, if surrounded, you can simply spin around in a circle while firing to eliminate all of your nearby foes, but with the Auto Shotgun, you'll take a long time to free yourself from an Infected circle.
 * Friendly fire can become an issue on higher difficulties. On Expert, you will almost always incapacitate a teammate if you accidentally hit them.
 * Against the Tank, the Auto Shotgun suffers a 25% damage penalty in Left 4 Dead, and a 15% penalty in Left 4 Dead 2.
 * In Left 4 Dead, if you expend every shell in either shotgun, it will take slightly longer to reload due to pulling back the charging handle/pumping the shotgun when it is ready to fire.
 * In order to be effective, you need to get up close and personal, which is especially dangerous for Special Infected because by the time you're in effective range, you're probably under attack by the Special Infected's ability.

Tactics

 * Generally refrain from shooting targets at long-range unless on Easy. This is an up-close-and-personal weapon and needs to be used as such to be effective. Wielders of shotguns should be given point to maximize its power. At longer ranges, wielders should switch to pistols to engage the targets.
 * On Normal and Advanced, the Auto Shotgun can yield decent results at mid range, though the spread generally keeps it from being effective against Special Infected.
 * Spamming a choke point at close range with the Auto Shotgun is very effective against a Horde.
 * Do not hold down the fire key in this situation, as doing so will only waste ammo. Since one shot can kill multiple Infected, you only need to tap it.
 * It is also important to note that while the Auto Shotgun has a high rate of fire, firing indiscriminately with this weapon is not always a good idea, as doing so will eat away at your ammo supply rather quickly and can raise the possibility of undesirable results, such as friendly fire or startling a Witch.
 * The Auto Shotgun has a large cone of fire, making it easy for a careless player to hit teammates accidentally. If you're trying to hit Infected close to your teammate, keep the crosshairs off your teammate to hit the Infected with the spread.
 * On Expert mode in a campaign, if you're using the Auto Shotgun, be extremely careful! One close-range blast is fatal enough to incapacitate a teammate instantly. If a blast hits them when they're incapacitated, they're dead. Make sure you're not firing at a Horde or mistakenly attacking an ally on Expert when using the Auto Shotgun. Instead, consider using melee shoving against the Infected to get them off, or crouching and blasting them off with a Pistol.
 * In Left 4 Dead 2 however, the friendly fire damage is reduced so 2 shots are needed to incapacitate and 3-5 shots are needed to kill an incapacitated survivor.
 * Using a laser sight on the Tactical Shotgun may not improve your accuracy, but it can potentially reduce friendly fire, since others can see where you are aiming.
 * There are 11 pellets per shot, equating to 23 damage per pellet.
 * There will always have 1 pellet landing in the middle of the crosshair when shooting while crouched, this can be used to snipe a distant infected's head due to the fact they die instantly from headshots. However, this tactic is relatively ineffective against other threats due to low damage of individual pellets and high damage drop off over distance of the shotgun.
 * A large number of Infected can be penetrated with a single shell provided they are lined up conveniently.
 * The Auto Shotgun does penetrate walls, and a teammate being mobbed behind a wall or door is easily protected by shooting at them through it. Its stopping power is minimized when doing such, but it is the easiest way to protect a teammate without risk of injuring them.
 * If you reload with an empty magazine, you will do a cocking animation during the reload, extending it by a second. A smart way to avoid this is to reload every chance you get, and melee if your ammo supply reaches one shot left. Since the shotgun loads a shell every half second, using this tactic can keep you shooting without having to wait through the reload sequence.
 * You can still shove while reloading, which will help if you find yourself in this situation.
 * As you can interrupt the reloading animation to fire, develop a habit of reloading every time you fire a shot. The only reason you should not do this if you need to go full auto with the shotgun (which should rarely, if at all, happen). The Auto Shotgun will block a good portion of your screen and move the flashlight away during reload, but you can simply manipulate your screen to compensate for the lack of light.
 * If you are caught reloading by a random Horde, the safest thing to do on harder levels of difficulty would be to melee until you are finished reloading.
 * If fighting a Horde, you can empty the shells from the Auto Shotgun and then switch to your melee weapon to finish the remaining Common Infected off. However, since both weapons have a very short range, you will have trouble fighting long range Special Infected such as Smokers and Spitters with satisfactory effectiveness. Use this combination when you expect to fight in close quarters combat.
 * Using this weapon in combination with the Magnum Pistol can be useful, giving you a powerful ranged attack to use against single Common Infected and a good close-quarters weapon to use if you get swamped by the Horde, though the low capacity of both weapons, and the fact that your primary weapon already does high damage, makes the dual pistols preferable.
 * It is not wise to shoot continually at a Horde, as this will eat up ammo extremely fast. Instead, pick your target, then fire one shot (it should be enough to kill it), rinse and repeat.
 * You can fire it faster by quickly tapping the fire button, rather than holding it down. This is useful against Tanks and other Special Infected, minus the Boomer, at very close ranges. It can also prove effective against large Hordes.
 * Be careful not to aim anywhere near gas cans or other carriable explosives that you don't want to ignite, especially in Left 4 Dead 2's The Atrium, The Port, and Scavenge mode. The Tactical Shotgun's spread can easily cause pellets to spray towards unintended targets so long as they are still in front of the shooter.

Left 4 Dead 2
The Auto Shotgun returns in Left 4 Dead 2 with new animations, now referred to as the Tactical Shotgun. Its reserve has been reduced from 128 to 90, it does 33 less damage per shot total, and the Survivor always pulls the lever on the side when they finish reloading, as opposed to only when the magazine is empty. Compared to its new counterpart, it has a wider spread, less damage per pellet, and more pellets per shot.

Unlike previous games. This weapon cannot incapacitate a full health survivor with one shot on expert, although the damage is still fatal enough on that difficulty.

Behind the Scenes
The Auto Shotgun is based on Counter-Strike XM1014 automatic shotgun. Its "price" in the gun's weapon file is the same as the XM1014's, and it references the XM1014 in its "animation" listing.

Early footage shows that the Auto Shotgun used unmodified XM1014 sounds. A video of the Auto Shotgun using the XM1014 sounds can be seen here.

According to the Auto Shotgun's weapon file, it used to have a larger spread, less accuracy, fired two less pellets and had a 9-round magazine.