A shotgun is a long arm roughly the size and weight of a rifle, but unlike the rifle (which shoots one projectile at a time), a shotgun fires variously-sized "shot" in a pattern that spreads the further it flies. Combat shotguns are meant for powerful blasts in closer range combat, or CQB. Another key difference from its cousin, the rifle, is that the shotgun's barrel typically isn't rifled; the inside of the barrel is smooth (also known as a smoothbore.) The shotgun can fire either a load of larger, ball bearing-sized pellets called buckshot, a load of smaller pellets called birdshot, or a solid hunk of lead called a slug. There are many different kinds of shotgun actions, but pump action is by far the most popular in the United States. However, there are also single-barreled break action, double-barreled break action (both over-under and side-by-side varieties), bolt-action, lever-action, and semi-automatic versions that one might encounter as well.
The most common shotgun gauges are 10, 12, 16, 20, 28, and 410. The smaller the gauge, the larger the diameter of the bore. 12 and 20 gauges are the most common - especially within the United States - and are both exceptionally powerful. It is also a good budget-minded choice. At some local stores, a 250-round case of 12 gauge ammunition can be purchased for around $70, and these cases are quite abundant. The same can not be said for the other gauges, though lead bird shot is typically the least expensive.
Shotguns rarely have a large magazine capacity so reloading is frequent and usually slow. They are also very loud, strong recoil, making them challenging and intimidating for beginners to fire.
Break-action shotgunsPopularized by Mad Max and Western movies, break-action shotguns have hinged barrels, and are reloaded by opening the hinge and exposing the breech, allowing for used shells to be manually removed, or ejected out by a spring, and unfired shells to be inserted. Break-action shotguns usually hold one or two rounds, corresponding with the number of barrels that are mounted on the gun. These are arguably the most simple type of modern firearm design, and are likely to be fairly easy to find and are easily attained due to their low cost. Break-action shotguns are simple and sturdy, but their relatively low capacity of one or two shells and the lengthy process of reloading - though reloading can be expedited with training and practice. Break-action shotguns are usually as long as most full length rifles, making them excellent for longer range hunting, but this trait also makes them difficult to maneuver in tight spaces. Shotguns (particularly break-action shotguns) are sometimes modified by shortening the barrel and removing the stock, making the weapon significantly lighter and more compact, at the price of a shorter effective range and poorer accuracy. Such a shotgun is said to be "sawed-off" but the legal term is "short-barreled shotgun" or SBS. Due to the popularity of such weapons with criminals in the past, this style of shotgun is either illegal or highly restricted in most jurisdictions.
Most break-action shotguns have their two barrels laid out side-by-side, but some have the two barrels one above the other. This is called an "over and under" shotgun, but occasionally referred to as an "over-under" or "O/U" shotgun. These are very popular with sports shotgunners because they are very well-balanced, though professional shooters usually have the shotgun carefully fitted to them. "Over-under" shotguns can be very expensive - Browning and Beretta O/U can often exceed $2000 USD.
A break action shotgun is a good choice as they are powerful, simple to operate and require little maintenance. However, the trade-off is the relatively low shell capacity, at one or two shotgun shells. A break action is not exactly the best choice, but not a bad one either; it beats throwing rocks any day of the week. If you find one, take it until you find a better weapon.
Lever-Action ShotgunsLever-action shotguns operate on the same principle as their lever-action rifle kin -- the operation of the weapon is performed by the "lever" that also constitutes the trigger guard. While they are not nearly as common in North America or Europe as break-action or pump-action shotguns, they have replaced pump-actions as the home defense shotgun of choice in Australia due to the gun laws there, which prohibit the vast majority of Australia's licenced firearm owners from legally owning pump-action shotguns and any semi-automatic longarms. In North America, the popularity of "lever-action" shotguns is beginning to rise.
Lever-Action shotguns are very similar to pump-action shotguns, in that a tube underneath the barrel holds the shells, and the lever operates the bolt, which when operated performs several tasks in conjunction. When opened, the bolt moves back in the receiver, the extractor of the bolt removes the shell inside of the chamber (unload), cocks the trigger and hammer, and strips an unfired shell out of the magazine tube, staging it to be loaded into the chamber. When the lever is lifted, closing it, the bolt slides forward, locking this unfired cartridge into the chamber, making the shotgun ready to fire. If the shooter squeezes the trigger, the hammer falls, firing the shotgun, and unlocks the action so that the cycle can be repeated. Lever action shotguns hold 5 shells in the magazine tube, though this depends largely on what "gauge" the shotgun is chambered for - .410 shotguns occasionally hold more.
Pump-Action ShotgunsPump-action shotguns have a single barrel, which is mounted above a tube magazine, into which shells are inserted. New shells are chambered by pulling the pump handle attached to the tube magazine toward the user, then pushing it back into place to chamber the cartridge. This action simultaneously projects the most recently fired shell out of the ejection port. Pump-action shotguns can be considered the most common type of shotgun. They are often used by civilians for hunting, skeet shooting and home defense and can be fired as fast as the user can pump the slide and pull the trigger. Reloading is a fairly slow process, but has the advantage of retaining firability, that is, a pump action shotgun may be fired and loaded at about the same time.
Some strange models, such as the "Remington 1740", have two barrels and one stock. These are much heavier, and more unwieldy than their single-barreled counterparts. If you do find one of these take it, until you find a single-barrel pump, or something more user friendly than a 15+ pound beast of a gun. Older shotguns such as the Winchester 1897 are capable of "Slam-Fire", A technique which allows the user to hold his/her trigger-finger down and pump-to-fire the gun, without ever having to take their finger off of the trigger.
A common shotgun is the remington 870. It is reliable, available, inexpensive and popular. this allows availability of service and modifications.
Semi-Automatic ShotgunsSemi-automatic shotguns, like semi-automatic rifles, fire a single shell each time the trigger is pulled, they then automatically eject the spent cartridge, chamber a fresh cartridge from the magazine, and are immediately ready to fire another shot. Besides this difference in operation, many semi-automatic shotguns are very similar to pump-action shotguns, with a single barrel and a tube magazine. Some of these shotguns can be operated both in semi-automatic and pump-action. The Franchi SPAS-12 and Benelli M3 Super 90 are both examples of semi-automatic shotguns with a conventional layout, and the former can also be operated as a pump-action shotgun. Other semi-automatic shotguns, such as the Saiga-12, have a layout more like that of a rifle, and use detachable box magazines. Still others, such as the Korean USAS-12, use other methods, such as drum magazines. The "Saiga-12" is becoming more popular with civilian gun owners, because of its increasing reliability and function strait from the factory.
Automatic ShotgunsAutomatic Shotguns continuously fire while the trigger is held, unleashing a devastating (but ultimately, excessive and impractical) flurry of fire. One such example of an automatic shotgun is the AA-12. They are extremely rare. These firearms can fire fully submerged in water and require less cleaning and maintenance than semi-auto shotguns. The "AA-12" variant of automatic shotgun has many shock-absorbing springs, the recoil is less than that of a regular 12-gauge shotgun. These can be fired one handed if needed. If you do find one of these rare firearms take it. It may be excessively easier to fire than any of the above mentioned. Another, even rarer automatic shotgun is the MK3A1. However, this is a mere prototype with only a handful in current existance. It is well worth getting your hands on, and is a tier more accurate than the AA-12 and the weight makes recoil nearly non-existant, and if one finds it by chance, they need not be experienced, though basic firearm training would help. The AA-12's advantages over the MK3A1 is particularly the ability to become semi-automatic, in which case the recoil is the lightest ever chambered for a firearm firing 12-gauge shells. Perhaps the most effective automatic shotgun is the Korean USAS-12, or ideally, the USAS-20. These variants use standard rounds, but the extreme weight of them diminishes recoil to the point of non-existence. Heavyset or not, the sheer weight makes mobility a challenge, and the rate of fire in any automatic shotgun will leave you out of ammo in only a second or two.
Effectiveness against zombies
Although glamourized as perfect zombie killing firearms, the reality is shotguns are often sub-par to rifles. Their effective range is very short with buckshot and moderate with slugs. The recoil on most shotguns can be substantial, and can be quite painful to unskilled shooters.
However, a shotgun's main perk is its undeniable stopping power and unrivaled versatility. With the correct ammunition loaded and a trained/experienced shooter the shotgun can potentially became highly effective in dispatching zombies. Due to most buckshot being composed of anywhere from 8 to 20 pellets per shot, it can give the shooter a much higher chance of killing zombie at close range. The fact that it can be loaded to hunt birds to elk, and everything in between, and that it can be loaded with specialty shells, makes it the Swiss Army Knife of firearms.