Guns 101

Knowing the basics of firearms can inform conversations with at-risk patients and help them stay safe

Firearms come in many shapes and sizes, with different features that allow for different operation and use.

Clinicians cite lacking knowledge of firearms as a barrier to talking with patients about risk and safe firearm practices. Clinicians don’t have to be firearm owners or have experience with firearms in order to talk to patients about how to be safe with them, just as they don’t have to be smokers to talk to patients about the risks of smoking. However, if clinicians don’t have experience with firearms, learning some basics can help them have informed conversations and make knowledgeable and appropriate safety recommendations.

The term “gun” refers to a broad category of devices that propel a projectile, including BB guns, airsoft guns, and paintball guns. A firearm is a type of gun that utilizes an explosive charge (gunpowder), also called a propellant, to fire a projectile. The term “gun” is colloquially used to refer to firearms.

Click below to learn about types of firearms and ammunition.

People own handguns predominantly for protection, often because they’re small and concealable. More than half (57%) of handgun owners in California own handguns at least in part for protection against people. Eight percent own handguns for collections, and 5% own for protection against animals.1

Most handguns are one of two types: semi-automatic pistols or revolvers. Pistols and revolvers use generally the same kind of ammunition.


The most common type of handgun is the semi-automatic pistol. “Semi-automatic” means that after the trigger is pulled and the gun is fired, a new round of ammunition goes into position, and another trigger pull will fire the gun again.

A 9mm semi-automatic pistol.
A 9mm semi-automatic pistol.

Pistols come in a wide variety of sizes. Common pistols include the .22-caliber and the 9mm. Caliber describes the diameter of the bullet, given in hundredths of an inch or in millimeters.

Pistols have ammunition magazines that eject from the bottom of the firearm. These magazines hold cartridges (rounds of ammunition) and feed them one by one into the chamber each time the pistol is fired. Typically these magazines hold between eight and 19 cartridges at once.

A pistol’s magazine release mechanism.

Pistol magazines are loaded by inserting cartridges one by one into the detachable magazine while it’s not in the gun.

Loading a pistol magazine.


Revolvers are a less common type of handgun. Revolvers can be single action, meaning the user must “cock” the gun by pulling back the hammer each time before firing, or double action, where pulling the trigger will rotate the cylinder, pull the hammer back, and fire the gun all in the same motion.

A .41-caliber magnum revolver.

Revolvers don’t have ammunition magazines but instead hold ammunition in rotating cylinders. Revolvers commonly hold six cartridges at once.

Loading a revolver.

People own long guns for various reasons. In California, sport shooting is cited by 34% of long gun owners as a reason for ownership. Hunting is the next most common (19%), followed by protection against people (18%).1 People use long guns to hunt a variety of animals, from birds, like pheasants and ducks, to big game, like elk.

Long guns are either rifles or shotguns. Rifles and shotguns have important differences and use different types of ammunition.


Rifle have long barrels, which result in an increased velocity of the projectile and afford users more accuracy than do shorter-barreled firearms, like handguns. Common calibers of rifles include .22-caliber, .223-caliber (the caliber of the commonly known AR-15), and .308-caliber.

A .223-caliber bolt-action rifle.

Rifles have one of a variety of actions — the method or mechanism by which a cartridge is placed in the chamber before firing and removed from the chamber after firing. Common rifles are single shot (i.e., require that the user load and “cock” the gun before each shot), bolt action, lever action, pump action, or semi-automatic. All these action types except semi-automatic actions require the user to manually or mechanically extract and insert cartridges.

Rifles typically use similar but more powerful cartridges than those used in handguns. Different types of rifles have different ammunition capacities, ranging from one to 20 cartridges. The rifle below uses a detachable magazine that holds its cartridges.

A bolt-action .22-caliber magnum rifle that uses a detachable magazine.


Similar to rifles, shotguns have long barrels that vary in length and diameter. However, shotguns use different kinds of projectiles in their cartridges (called “shells”) than handguns and rifles do, usually a group of pellets (called “shot”), as discussed below. Shotguns’ long barrels help the shot gain velocity. Shotguns have a “choke” on the muzzle, like a nozzle on a hose, that decreases dispersion of the shot.

Shotguns have one of several action configurations. Shotguns are commonly single-barreled, double-barreled, pump action, or semi-automatic. Single- and double-barreled shotguns require the user to hinge the barrels open to eject and manually insert ammunition. With pump action shotguns, the user pumps the forend to eject and insert a new shell. Double-barreled shotguns, which have “break actions,” can be side by side or one atop the other (referred to as “side-by-side” and “over-under,” respectively).

A 20 gauge over-under break action shotgun.
Opening the action and inserting shells into a 20 gauge over-under break action shotgun.

Shotgun ammunition capacity ranges from one to about 10, but typically shotguns hold five or fewer shells at once.

Many firearms are semi-automatic, which means that after the trigger is pulled and the firearm is fired, a new round of ammunition goes into position in the chamber. This new round won’t be fired until the trigger is fully released and then pulled again. Compared to guns that are manually operated, semi-automatic firearms generally allow faster repeat firing.

Fully automatic firearms are also known as machine guns. Similar to semi-automatic firearms, after an automatic firearm is fired, a new round of ammunition goes into position in the chamber. However, unlike semi-automatic firearms, there is no halting process that requires the user to release and pull the trigger again to fire another round. Automatic firearms can continue firing until the trigger is released as long as ammunition is available. Though functionally different by design, some semi-automatic rifles are indistinguishable in appearance from fully automatic rifles.

Semi-automatic firearms are common and are owned by civilians for protection against people, hunting, and sport shooting. Automatic firearms are tightly regulated, at the federal level and by many states. California law prohibits the possession, manufacture, and sale of automatic firearms without a permit. Automatic firearms were invented for combat and civilian ownership is rare.

There is no unanimously accepted definition of an assault weapon or assault rifle; the term is controversial and its definitions contested. Semi-automatic firearms that are capable of accepting detachable magazines and have “military-style” features, such as collapsible stocks or pistol grips, may be referred to as assault weapons. The “AR” in AR-15 is commonly assumed to stand for “assault rifle” but actually stands for ArmaLite rifle, for the company that developed the AR-15.

The two most common types of ammunition are cartridges, which contain bullets and are used in handguns and rifles, and shells, which contain shot and are used in shotguns.

Handgun and Rifle Cartridges

Bullets are fired out of cartridges used in handguns and rifles. Cartridges are commonly but mistakenly referred to as bullets, but a bullet is just one component of a cartridge.

Handgun and rifle cartridges have four components:

  • a case, usually made of brass, steel, or copper
  • a primer (which ignites the propellant)
  • gunpowder (the propellant)
  • a bullet (the projectile)
Components of handgun and rifle cartridges.

Handgun cartridges come in a variety of sizes to suit different kinds of pistols and revolvers.

Common handgun cartridges. From left to right: .22-caliber rimfire, .32-caliber centerfire, 9mm centerfire, .45-caliber centerfire, .41-caliber magnum, and .480-caliber centerfire.

Similarly, rifle cartridges come in a variety of sizes to suit different kinds of rifles.

Common rifle cartridges. From left to right: .22-caliber rimfire magnum, .223-caliber centerfire, 6mm benchrest, 6mm Remington, .240-caliber Weatherby magnum, 6.5/06, .284-caliber, .338-caliber Winchester magnum, and .458-caliber Lott. The names in these labels (i.e., Winchester and Weatherby) are for the companies that manufacture these types of firearms and ammunition. “Benchrest” refers to a specific type of rifle shooting where the user sits at a bench and rests the rifle rather than holding it. “Centerfire” and “rimfire” reflect the two possible positions of the primer inside the cartridge.

When a handgun or rifle is fired, the bullet itself gains speed before it exits the barrel. After firing, the empty case is removed or automatically ejected from the action.

Shotgun Shells

Shotgun cartridges, called “shells,” are generally made up of the same components as handgun and rifles cartridges but contain a different kind of projectile and also include a wad to separate the gunpowder from the projectile. The components of a shotgun shell are:

  • a case, usually made of plastic with a thin covering of brass on the base
  • a primer (which ignites the propellant)
  • gunpowder (the propellant)
  • a wad (to separate the powder from the projectile)
  • a group of shot or a slug, usually made of lead or steel (the projectile)
Components of a 12 gauge shotgun shell.

The diameters of shotgun shells, which are different “gauges,” vary to fit shotgun barrels of different diameters. Shotgun shells with smaller diameters have higher-numbered gauges than those with larger diameters.

When a shotgun is fired, shot is passed through the barrel and ejected, at which point it spreads into a pattern. Different sizes of shot are used for different purposes: for example, if hunting, larger “buckshot” may be more appropriate for larger animals, rather than smaller “birdshot.” A slug, one large pellet typically made of lead, may be used instead of shot, if hunting large game animals like deer.

Common shotgun shells. From left to right: .410-caliber, 28 gauge, 20 gauge, 16 gauge, 12 gauge, and 3-inch magnum 12 gauge.
A comparison of types of shot. The larger, silver-colored shot on the left is no. 4, which could be used for hunting larger birds, like pheasants or ducks. The smaller shot on the right is no. 7.5, which is typically used for target shooting or for hunting small birds, like quail.

Almost all firearms have intrinsic safety mechanisms that help prevent them from being unintentionally fired. Generally, a firearm’s “safety” is a lever that blocks the firing mechanism in one of a variety of ways. Some guns have safeties that may be turned off with the user’s thumb before firing. Others have grip or trigger safeties, which require that the user depress part of the grip or trigger to be able to pull the trigger and fire the gun, lowering the chances that the gun can fire accidentally.

Prototypes of personalized or “smart” guns, equipped with intrinsic devices to prevent unauthorized use, may be promising but these guns are uncommon in the US. Smart guns’ embedded features can include biometric technologies like fingerprint or iris scans, magnets or radio-frequency identification (RFID) technology, or intrinsic combination locks.

Intrinsic safety mechanisms, because they can be disabled by unauthorized users, aren’t sufficient to prevent firearm-related harm. Firearms should be safely stored: kept unloaded and locked up using a locking device.

To reduce the risk of firearm-related harm for everyone in the home, all firearms should be stored locked up, unloaded, and separate from ammunition.

Firearm owners use different types of firearms and ammunition for a variety of purposes, including for hunting, protection against people, sport shooting, and collecting. Firearms can be part of someone’s identity and, for some owners, firearms may have a symbolic cultural meaning, such as an association with freedom, protection, or self-reliance.

Those interested in participating in general firearms safety training can get in touch with local gun ranges to see what training is offered and to sign up.


Page last updated October 2020.

  1. Kravitz-Wirtz, N., Pallin, R., Miller, M., et al. (2019). Firearm ownership and acquisition in California: Findings from the 2018 California Safety and Well-being Survey. Injury Prevention.
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