For an explanation of kinds of shotguns, go
here. This page is a guide to different types of shotguns, their care, and their usage. If you are looking for information about a specific model, check out the
review page. Shotgun specific tactics can be found
here. Feel free to add to it if you find a gun that hasn't been added. The format for entries is below:
Model: This model number of this year. Tell the gun's story.
Where to find:
Who uses it and where would you find it? How are replacement parts?
Complexity:
How hard is it to maintain and use this weapon effectively?
Size and weight:
Barrel length, overall length weight in ounces and kilograms.
Action:
Is it autoloading? Single shot?
Caliber(s):
Primary chambering as well as other variations.
Magazine:
Type of magazine and capacity.
Trigger:
Trigger type and weight if available.
Controls:
Where the safeties, action releases and other controls are on the weapon, with pictures if possible.
Loading: How to load the firearm and make ready to fire.
Condition One, or "Locked and Cocked." Chamber loaded, magazine full, hammer cocked and safety applied.
Condition Two. Chamber loaded, magazine full, hammer down, safety off.
Condition Three. Chamber empty, magazine full, hammer down, safety off.
Unloading:
How to unload and make safe.
Field Stripping:
How to take down the weapon for cleaning, with pictures if possible.
Design Quirks:
Unique aspects of this gun. 
Model: Remington 870
The Remington 870 holds the record for best-selling shotgun in the world. It was first manufactured in 1951 and sales have been steady since, with over 10 million guns having been produced. It's in use with police and military organizations worldwide and is just as popular for hunting, self-defense, and sport shooting.
There are six basic types of 870:
Wingmaster shotguns are blued steel with high gloss or satin walnut stocks.
Police shotguns are blued or parkerized steel with satin walnut or synthetic stocks. All of the parts are heavy-duty and receive extra care and inspections during assembly.
Marine shotguns are nickel-plated with synthetic stocks.
Express shotguns are matte black bead-blasted with laminated hardwood or synthetic stocks, and cheaper.
Super magnum shotguns are chambered for 3 1/2'' 12 gauge shells.
XCS shotguns have TriNyte-coated external metal with nickel-plated internals and speedfeed stocks.
All can be given bead, double bead, ghost ring, or adjustable open sights. All can be given cantilever and receiver mounts for scopes and reflex sights.
Where to find:
As stated above, the shotgun is extremely common worldwide. Police and military forces across the globe make good use of the gun, and it's just as common among civilian households. With over 10 million shotguns, it's not hard to get one. They're available in the majority of firearms shops, especially in the United States, and can be found for less than $300.
Complexity:
Though not a simple as a break open shotgun, the gun is quite simple and has less moving parts than most designs. The controls and action are quite similar to the Remington 7600 series of pump-action rifles, so any shooter familiar with those can quickly learn to operate an 870. There are relatively few controls compared to a handgun of similar cost, and the general format is used on a multitude of other designs.
Size and weight: Weight 112 ounces (3.2 kg) to 128 (3.6 kg) unloaded. Length 946mm to 1,283mm. Barrel 457mm to 762mm.
Action:
Pump-action.
Caliber(s):
12 gauge, 16 gauge, 20 gauge, 28 gauge, or .410
Magazine:
Tubular magazine under the barrel. 3-8 rounds.
Trigger:
6-8 pound pull, can be reduced to 2.5-3.5 pounds by a match grade trigger.
Controls:
Push-button safety behind the trigger (push from the right to fire, push from the left for safe). Slide release, or action release button is to the front right of the trigger, protruding down from the receiver. The slide release is far forward enough that you will need to release your shooting grip to actuate it.
The shell elevator or shell latch is spring loaded on Remington 870s, staying down during loading.
Loading: How to load the firearm and make ready to fire.
Condition One, or "Locked and Cocked." Chamber loaded, magazine full, hammer cocked and safety applied.
1) Point the gun in a safe direction. Critical step in case the gun accidentally discharges! 2) Ensure that the forend is in the fore-most position.
3) Take a shell with the brass end against your thumb.
4) Using the trigger guard as a guide, push the shell up and forward into the loading port until the rim of the shell engages the shell latches.
5) Continue loading until the magazine is full.
6) Firmly rack the forearm all the way to the rear, then forward, to chamber the first round.
7) Apply the safety if necessary.
Condition Two. Chamber loaded, magazine full, hammer down, safety off.
Impossible on a pump action shotgun.
Condition Three. Chamber empty, magazine full, hammer down, safety off.1) Point the gun in a safe direction. Critical step in case the gun accidentally discharges! 2) Ensure that the forend is in the fore-most position.
3) Take a shell with the brass end against your thumb.
4) Using the trigger guard as a guide, push the shell up and forward into the loading port until the rim of the shell engages the shell latches.
5) Continue loading until the magazine is full.
Unloading:
1) Point the gun in a safe direction.
2) Depress the action release.
3) Slowly slide the forend back until the front of the shell just clears the forward edge of the ejection port.
4) Remove the shell by hand.
5) Slide the forend all the way back to load the next shell.
6) Turn the shotgun to the right, letting the shell roll out of the ejection port.
7) Press the shell latch on the right side of the receiver to release a shell from the magazine through the loading port.*
8) Continue until the gun is empty.
9) Visually and manually inspect the chamber for any remaining rounds. In low light, feel inside the chamber and magazine tube for shells.
10) Point in a safe direction and pull the trigger. Hammer should snap onto an empty chamber.
*Alternatively, instead of operating the shell latch, the shooter can simply rack the forearm until the weapon is empty.
Field Stripping:
1) Point the gun in a safe direction and unload it.
2) Unscrew the magazine cap by hand. If it gets stuck, wrap it with a cloth and use pliers. Hold onto the cap tightly, as it is spring-loaded and can pop off with force!
3) Slide the barrel off.
4) Flip the shotgun upside-down and press down on the spring-loaded metal strips on the forend from the inside of the opening until they're flat, and pull the forend and bolt carrier out like you did with the barrel.
5) Use a wooden dowel rod or other object the size of the pins (screw, nail, screwdriver, etc.) to tap out the pins on the trigger group. Slide the trigger group out from the bottom.
Reassembly
1) Slide the trigger group back into place and tap the pins back in.
2) Slide the forend in while holding the metal strips down.
3) Slide the barrel back on.
4) Insert the shell follower into the magazine tube, then the spring. Place the magazine cap over the spring and screw it on by hand until it will no longer move. Do not use pliers to screw the magazine cap back on, as the extra torque may damage the gun!
Design Quirks:
Unique aspects of this gun. 
The Rules - What you should know before reading these pages and handling weapons.
Firearms - A basic guide to different types of firearms.
Accessories - The add-ons that may just give you an edge in that gunfight.
Ammunition - An overview of types of ammo and reloading.
Weapons reviews - A user-created database of reviews for various zombie-slaying implements.
Handguns, Rifles, Shotguns, Heavy Weaponry - A user-created guide to using and maintaining firearms you are likely to come across.