How Shotguns Work

Winchester 12-gauge Super X2. See more gun pictures.
Photo courtesy Shotgun World

Shotguns first came into use in the early 1600s. The first two-barrel shotgun appeared in 1873, and the first modern, hammerless, pump-action shotgun was produced in 1904. By the turn of the century, they were immensely popular. Many military officers loved their personal shotguns so much that they brought them along instead of sidearms to World War I, earning them the nickname "trench guns." Since then, they have become a permanent part of the military arsenal and a part of the everyday lives of many civilians as well.

Why a shotgun instead of, say, a rifle? Well, to do its job, a projectile must:


  • make contact with the target
  • hit the target in a critical spot

With a wider stream of potentially deadly projectiles, a shotgun is like using a can of spray paint if a rifle is like using a felt-tip pen. As long as the target is within its effective range, a shotgun will give you a much better chance of making critical contact with one pull of the trigger.

The shotgun is the Swiss-army knife of guns. It is an indispensable tool -- on the farm, in combat and on the hunt. They are just as useful in non-lethal situations, like for scaring away pests or for opening locked doors in a police or military situation, as they are for big game hunting. In this article, you'll find out how shotguns work, what different types are out there and about the various types of ammo a shotgun can accommodate.

The Basics

Whether you're talking about a handgun, a rifle or a sho­tgun, all modern guns have to do some of the same things. They have to send ammunition flying out of a long cylinder called a barrel, and they have to allow for the loading and unloading of new and spent ammunition. When you pull the trigger, a hammer or firing pin strikes an explosive charge on the back of a cartridge or bullet. This causes a small explosion that changes the air pressure in the barrel, forcing whatever was in front of the explosion (such as a bullet or metal pellets) out the other side at an extremely fast speed.

Target practice

Shotguns are designed to fire batches of small projectiles instead of single bullets with each pull of the trigger. These projectiles themselves don't have to be aerodynamic like bullets and aren't expected to travel long distances. They are designed to cause their worst damage at closer ranges. Shotgun ammo comes in varying shapes and sizes and includes lead, steel and bismuth pellets, bean bags, rock salt and rocket-like sabots. Shotguns can also fire individual metal slugs.


Know Your Shotgun Parts

All shotguns have some of the same basic components. Starting from the end nearest to the shooter, there's often a stock that allows you to steady it against your shoulder muscles. Some manufacturers put a recoil pad at the end of the stock to help dampen the kick you feel when you fire it. There are some shotguns, usually "assault" style, that have foldaway stocks or no stock at all. Moving forward from the stock, you'll find all of the parts associated with firing. This includes the trigger that connects to the sear and hammer. Some shotguns have a pistol grip that extends downward below the trigger.

The hammer activates the bolt assembly and firing pin, which rests against the cartridge to be fired. Now we're at the chamber, where the loading, unloading and firing happens. The chamber can be accessible from the side or the top. Connecting to the chamber is the barrel, which is the long tube that the ammo travels through as it leaves the gun. Some shotguns have a magazine connected to the chamber -- this may take the form of a second, shorter tube below the barrel or else a drum or rectangular cartridge that snaps into the barrel. There may also be a fore-end (a sliding handle colloquially known as a pump) attached to the shorter tube, which is used to partially automate the loading and unloading process. On the top of the barrel, you'll often find a bump that's used as a crude sight.


Measuring Up: Gauge vs. Caliber

Shotgun sizes have always been measured in a somewhat roundabout way. You would think that the "12" in a 12-gauge shotgun corresponds to some linear measurement -- maybe inches or centimeters. But that's not the case. "12-gauge" means you can make 12 lead balls, each of equal diameter to the gun barrel, out of 1 pound of lead. This originated in the days when you would buy lead by the pound to make your own ammo. The gauge told you how many rounds you could make for the gun from 1 pound of lead.

The smaller the gauge number, the wider the barrel. The largest shotgun is a 4-gauge. The .410 shotgun, the smallest, is an exception to the rule: It's actually a .410-caliber -- it has a .41-inch barrel diameter.


In general, the smaller the barrel diameter, the less "kick" or recoil the shooter feels from the gun. Many experts say that a 20-gauge shotgun is a good beginner's gun because it has relatively little recoil but fires more shot per shell than the smaller-diameter .410-caliber.

Action and Barrel Types

12-gauge Winchester model 1200
Photo courtesy Integrated Logistics Support Center (ILCS)

Besides firing, another thing shotguns have to do is set a new cartridge in the chamber and get rid of what's left over from a cartridge that has just been fired. Over time, shotgun manufacturers have developed several different technologies to accomplish this. As new innovations have come along, most of the old designs have stuck around, though. Some of the simplest ways to accomplish the task are still the most effective and dependable.

One way individual shotguns differ in loading and unloading is in their anatomy. The vast majority of shotguns are either single-barrel, double-barrel side-by-side or double-barrel over-under.


The action, or method a shotgun uses for loading and disposing of cartridges, can be:

  • autoloading
  • pump action
  • break action
  • bolt action

In the following sections, we'll examine each of these action types.

Break, Bolt and Pump Actions

SKB Model 485 break-action shotgun
Photo courtesy Shotgun World

Break Action

Break-action shotguns are the most straightforward and the safest, and they're commonly used in shooting competitions. The gun has a hinged opening where the chamber meets the barrel. By opening the gun, it is easy to see if it's loaded or not.

To load a new cartridge, the shooter breaks open the barrel on its hinge, physically places a cartridge into the chamber and then closes it. In older model shotguns, the shooter would have to manually cock the hammer and pull the trigger. In most modern shotguns, there's no need to cock the hammer before pulling the trigger. In most cases after firing the gun, the shooter then manually removes spent cartridges from the chamber and repeats the process to fire again. There are both single-barrel and double-barrel shotguns that are break-action. On modern double-barrel shotguns, there's only one trigger and an automatic or manual barrel selector (the selector picks which barrel fires).


Bolt Action

Bolt-action shotguns are not all that common, but they work just like bolt-action rifles. The bolt is a rod attached to a spring, and there's a handle sticking out of it. To load a bolt-action, the shooter twists the bolt handle up and then pulls it back. This both exposes the chamber and cocks the firing mechanism. The shooter then loads a magazine into the chamber and pulls the bolt forward into place. This strips the top cartridge from the magazine, blocks it off from the magazine and prepares it for firing. After firing the first shot, each time the shooter pulls the action back and then forward it ejects the spent cartridge, strips the next cartridge from the magazine and prepares it for firing.

Pump Action

Pump-action shotguns also have a moving bolt; but instead of a handle, their bolt system is operated by a wooden or composite slide called the fore-end. In this case, the magazine is a shorter tube under the barrel. First, the shooter fills the magazine with three or more cartridges. There's tension in the magazine from a spring, It's a bit like putting D-cell batteries into an old flashlight. He or she then pulls the fore-end to the rear of the gun. This ejects anything that's in the chamber, cocks the hammer, and loads a shell in the chamber. Next, the shooter pushes the slide forward, which pushes the block and firing pin into the firing position against the cartridge. After each fired shot, the shooter repeats this motion to reload the gun and eject used cartridges.

An experienced shooter can repeat the motion of firing and then pumping to reload very quickly. And because the action is all mechanical and linear, it's very simple and unlikely to fail in action.


Autoloaders and semi-automatic shotguns take the pump-action idea one step further, using similar mechanisms to those employed by machine guns. As the designs get more complex and have more moving parts, the chances for operator error, misfire and jamming increase dramatically. Autoloaders are considered less reliable than pump-action and break-action guns.

Recoil-operated autoloaders use the force naturally generated by recoil from the firing process to eject the spent cartridge, get a new one from the magazine and ready it in the chamber. In this case, the explosion from the cartridge forces both the barrel and the bolt to travel a couple of inches backwards. This ejects the spent cartridge. The barrel and bolt hit springs that send them forward again, and the bolt strips a new cartridge into place on the way. The barrel and bolt lock back into place and are ready to fire again. There are also short-recoil systems that work similarly but with a greater separation between the movement of the barrel and the movement of the bolt.


The gas-powered variety of autoloaders work like assault weapons. For a detailed explanation of these systems, see How Machine Guns Work: Gas System.

Automatic Shotguns

There are automatic shotguns in limited use in the military, including the USAS-12 and the Franchi SPAS-15. These are rapid-fire, high-impact weapons, allowing the shooter to fire up to four shots per second with one pull of the trigger. The USAS-12 uses a drum magazine, and the SPAS-15 uses a box magazine.

Even more powerful is the Pancor Jackhammer, currently just a concept and prototype weapon. It's an automatic, drum-loaded shotgun made out of plastic. The Jackhammer is extremely light and has a remarkably small recoil. Most of the recoil energy is captured and used in loading and firing the next round. As an interesting additional feature, it is possible to take the drum magazine off the gun, attach a detonator and use it as an anti-personnel mine that fires all of the cartridges at once when tripped.


What's the Difference Between a Shotgun and a Rifle?

Handguns and rifles have rifled barrels, meaning that there are grooves cut lengthwise into the inside of the barrel. The grooves cause a bullet to spin, which makes it shoot out straighter and travel faster.

Most shotguns are not rifled inside. With standard ammo like lead or steel shot, a rifled barrel would cause the pieces of shot to bunch up into a tighter pattern, which would defeat the purpose of using a shotgun.


For shooters who to more tightly control the spread and impact point of their shot, there are chokes. These are tubes that use a cone or bumpy shape to taper the angle at which ammo leaves the barrel and the distance it travels. Some of them are rifled, and some are not. Some are even adjustable on the fly, meaning you can change the effect without removing the choke.

Choke manufacturers express their expected effects by listing the amount that a choke constricts the barrel and the percentage of shot that will hit a target area at 40 (or, in some cases, 25) yards. In general, the more the barrel is constricted, the higher the percentage of shot hitting the target at 40 yards. But this is all relative to the size and type of shot. Because of this and all of the variables involved (weather, wind conditions, individual barrel, etc.), it's not easy to say precisely how a particular choke will affect the shot pattern, and most shooters have to learn by trial and error.

Types of Ammo: Shot

Cartridges filled with shot are the most common type of shotgun ammo. Shot are little balls made of any number of metals, including lead, steel, bismuth, tin and zinc.

Each metal behaves a little differently. Lead has some properties that make it one of the most effective materials for shooting game and targets. It is relatively heavy and therefore maintains its explosive force well. It is also somewhat soft, so it changes its shape as it leaves the barrel. This gives it a more spread-out shot pattern than other materials but still delivers a great deal of energy. There is some evidence that because steel pellets do not deform -- they maintain their round shape throughout their flight -- they wound animals without killing them more often than lead.


Until the early 1990s, most shot was made of lead. As environmentalists studied its effect on the ecosphere, they found that the spent lead shot hunters left in waterways and forests had harmful effects on wildlife and risked contamination of drinking water. Lead shot has been banned from waterfowl hunting in the United States since 1992, and various types of steel and alloy shot have taken its place.

The rule of thumb for shot size is the higher the number, the smaller the diameter of the shot. There is a consistent standard in the United States, but worldwide the numbers don't correspond to any specific measurement across the board. At Chuck Hawks' Shot Pellet Information and Recommendations, you'll find a guide to the various sizes in the United States and what they are used for. In hunting, smaller ammo is used for smaller game, and larger ammo is used for larger game. Buckshot is large-sized shot that got its name because it is used to hunt deer. Because different materials have different weights and characteristics, shot size alone does not tell the whole story. For example, if you are shooting with steel, you'd have to use larger shot than you would if you were doing the same type of hunting with lead.

Types of Ammo: Slugs

Mossberg M590/590A1 combat shotgun (center)
Photo courtesy DVI

Slugs are molded chunks of metal, nylon or plastic. In effect, they turn a shotgun into a crude rifle. Slugs are fired individually, like bullets, instead of in bunches like buckshot and birdshot. They can come in a variety of shapes, but they are often tapered into a bullet shape. They can be solid or filled with substances like explosives or incendiary powder.

Shotgun slugs can be rifled -- this is supposed to make them spin in the air and thus improve their flight length and accuracy.


One reason hunters use slugs is to hunt deer in states that ban the use of rifles and/or buckshot ammo. The shotgun/slug combination provides a legal, if shorter range alternative. There are at least 20 states that have restrictions of this kind.

Non-explosive slugs are also used for crowd control. When deployed properly, they can act as a non-lethal deterrent in these situations. They are used in organized shooting competitions as well.

Types of Ammo: Sabots

A sabot is a specially shaped, two-stage cartridge. It has an outer jacket that helps it travel longer distances, and it has an inner slug or payload. The jacket is designed to fall away in flight after it reaches a certain distance. Several hunting sources suggest that sabot ammunition is only effective at longer distances when shot through a rifled barrel. For a shotgun hunter, this usually means adding on a rifled choke tube.

Sabot can also describe an arrow-like shape of material that fits in a standard shell. One particularly frightening sabot-style payload is the flechette. A flechette round contains hundreds of small, needle- or razor-like projectiles designed to penetrate armor and inflict painful wounds. They are banned by the Geneva Convention but do still see use in combat and counter-terrorism from time to time.


Shotgun Laws

Although there are laws in the United States about purchasing, selling, using and carrying shotguns, these are actually less regulated than most types of guns. Gun-related activity is regulated by the Federal Bureau of Alcohol, Tobacco, and Firearms (BATF). Here are some of the federal laws that apply to shotguns:

  • Buying restrictions: Certain classes of people are not allowed to purchase shotguns. This includes felons, fugitives, minors under 18, the mentally ill, dishonorable discharges from the armed forces, those under a court order and perpetrators of domestic violence.
  • Selling restrictions: Sellers must have a federal firearms license or sell through a dealer with a license. They must be licensed by several federal agencies, including the BATF and the Department of Justice. Shotgun sales must be documented with federal form 4473, which maintains the purchaser's information and the gun's serial number. These laws do not apply to antique firearms.
  • Short-barreled shotguns: The National Firearms Act (NFA) of 1934 makes it illegal to own shotguns with barrels less than 18 inches in length unless they are specifically registered as such with the federal government.

States also have their own firearms laws, which can include waiting periods before purchase, separate registration requirements and bans. See NRA-ILA: Compendium of State Firearms Laws for a general reference to the gun laws in each U.S. state.


For more information on shotguns and related topics, check out the links on the next page.

Lots More Information

Related HowStuffWorks Articles

More Great Links


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  • Hawks, Chuck. "Shotgun Action Types."
  • Hawks, Chuck. "Shotgun Slugs."
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