In-Depth Explanation of Firearms and Ammunition

May 28, 2021
In-Depth Explanation of Firearms and Ammunition

According to recent estimates, the number of firearms in worldwide circulation is over 1 billion; 85% of these firearms are in the hands of civilians, and over 400 million of these firearms are in the United States. Let’s discuss the basics of firearm operation, the different elements of guns and ammunition, a list of the most common types and categories, and a brief overview of common gun terminology.

Who Uses Firearms and Why: A Basic Primer

No matter which category of society an individual belongs to, firearms are relevant. They serve important functions as part of both recreation and national defense. For law-abiding civilians, the firearm has many applications: personal protection, hunting, competition, recreation, family traditions, and more. Of the 1 billion firearms in worldwide circulation today, over 85% are legally owned by civilians. Criminals and people outside of the law use firearms to protect themselves or carry out illegal activities. According to the Stockholm International Peace Research Institute, the global arms trafficking market is worth at least $95 billion. Firearms are also the primary standard-issue personal weapons in law enforcement, military, correctional facilities, and many other armed uniformed services. Agencies and departments of all sizes carry guns as a duty weapon, from small-town municipal police to elite special forces units. The Small Arms Survey estimated in 2017 that at least 393 million firearms were in the hands of American citizens. However, it is highly likely to be well above 400 million. With a population of 331.44 million as of April 2021, this corresponds to over 120 guns for every 100 people.

Basics of Firearms

A firearm is a ranged weapon designed to launch one or more projectiles at high velocities from a tube (the gun barrel), allowing the shooter to hit distant targets with great accuracy. Firearms exploit the energy created by chemical propellants (gunpowder) to fire projectiles. Upon ignition, the gunpowder generates a high amount of pressure contained within the barrel and channeled toward the muzzle. This pressure accelerates the projectile down the barrel and launches it at a high velocity towards the target.

Parts of a firearm

Although the exact number and types of parts found on a gun largely depend on its design and category, all firearms feature three essential components and elements critical to their function:


Also known as the receiver, the action is the heart of the firearm. A firearm action contains the trigger and the mechanisms used to load, fire, eject, and unload cartridges (e.g., bolt, slide, extractor, ejector, firing pin). There is a wide variety of action types, each with its own features and elements. All actions feature at least one trigger, although some designs may feature more than one.


The barrel is the gun’s shooting tube. Typically made out of high-strength steel, the barrel contains the pressure generated when firing a cartridge and guides the projectiles towards the muzzle (and, by extension, the target). A barrel comprises three parts:

  • Chamber: The back end of the barrel, into which ammunition cartridges are loaded.
  • Bore: The hollow part of the barrel through which the projectiles travel.
  • Muzzle: The front end of the barrel, out of which the projectiles exit.

Most gun barrels possess grooves (rifling) designed to impart spin on the projectiles, allowing them to stabilize in flight, achieving long and accurate trajectories.


Also called shoulder stock, the stock is an element designed to rest against the shooter’s shoulder. The purpose of a stock is to aid the shooter with aiming and absorbing recoil.

Basics of Ammunition

The proper designation for a single unit of ammunition is a cartridge, although many colloquial terms, such as rounds or shots, may also be employed. Shells is also commonly used, mainly referring to shotgun cartridges. Do not refer to a single unit of ammunition as a bullet; this word refers to the projectile, not the entire cartridge.

Parts of a cartridge

A typical ammunition cartridge comprises four elements: the projectile, the case, the propellant, and the primer.


The projectile is the part of a cartridge designed to travel down the barrel and hit the target. Pistol and rifle cartridges generally only hold one projectile per round: a bullet. Shotgun cartridges are the most common firearm that does not hold only one projectile. Shotguns can use both slugs and shot pellets. Slugs are a singular large projectile, while shot pellets are many small, usually spherical projectiles.


The case (or casing) is the part of a cartridge containing all of the other elements together. Shotgun cases are typically called hulls. A typical modern pistol or rifle case is made of brass or steel, or more rarely, aluminum or polymer. Shotgun cases are more commonly known as hulls. Modern shotgun hulls typically use a plastic casing with a brass or steel case head. The older shotgun hulls more commonly had paper or cardboard instead of plastic.


The propellant of a cartridge is essentially the charge of fuel contained within each cartridge. Although ammunition of the past employed black gunpowder (also called blackpowder), a low explosive compound consisting of sulfur, carbon, and potassium nitrate, this propellant type is now considered obsolete. All modern ammunition employs various types of smokeless powder, which are more powerful and produce less residual smoke than blackpowder.


If you could compare the propellant in ammunition to the fuel in a car, the primer is the equivalent of a spark plug. Modern firearms cannot directly ignite the propellant inside a cartridge case; the function of the primer is to facilitate propellant ignition. The primer is a small, button-shaped circular part found inside the head of a cartridge case, designed to be struck by a firing pin. Primers are made of copper or brass and contain a small quantity of shock-sensitive explosive chemicals, typically lead styphnate. Upon impact, the shock-sensitive compound immediately deflagrates, producing enough heat to ignite the propellant in the case, in turn generating a high quantity of pressure, pushing the bullet out of the case, through the barrel, and out of the muzzle. Rimfire cartridges do not feature separate primers; instead, the rim of a rimfire cartridge contains a priming compound designed to be struck by a firing pin to achieve ignition.

Common Firearm Features and Elements

Firearms exist in different shapes and designs, each with its own range of features and elements. Two features that are present in almost all modern firearms are magazines and safety mechanisms. While these are unnecessary for a weapon to be classified as a firearm, they are common because they provide ease of use and user safety.

Magazines and feeding systems

The magazine is the ammunition storage device of a firearm. Every time the shooter fires or cycles the action, the magazine brings a fresh cartridge into the action, allowing the mechanism to push that cartridge into the barrel’s chamber. Typical magazines are detachable and box-shaped, allowing the shooter to carry multiple spare magazines on their person. When the magazine in their firearm runs empty, the shooter can quickly replace it with a fully-loaded magazine. Some magazines are integral to the firearm, requiring the shooter to insert fresh ammunition by hand, one by one. A magazine may be box-shaped (ammunition sits in a vertical column), tubular (rounds sit horizontally, end to end), or rotary (ammunition stored in a spiral-shaped tube). Some firearms do not employ magazines to hold ammunition, employing elements such as cylinders (e.g., revolvers) or ammunition belts (e.g., machine guns) instead.

Safety mechanisms

Under normal conditions, a firearm should only fire when a shooter presses the trigger. The safety mechanisms on a gun exist to prevent it from firing unintentionally, accidentally, or negligently. There are two types of safeties: active and passive.

  • Active safety devices must be manually activated and deactivated by the shooter. Examples include safety buttons, levers, key-operated trigger locks, or the SAFE setting on a fire selector.
  • Passive safety devices engage automatically when the gun is not in use, only disengaging when the shooter grips or uses the firearm under normal conditions. Examples include grip safeties, the Glock Safe-Action trigger safety system, firing pin blocks, transfer bars, magazine disconnects, and many more.

It is also possible to install external safety systems on a firearm. An external safety system is a device that is not part of the firearm inserted into or around the gun to prevent unauthorized people from using or shooting it. Examples include cable locks and trigger locks.

Gun Safety

All firearm owners and operators should follow the rules of gun safety as strictly as possible. Although these rules may seem redundant, it is critical to respect them at all times to avoid severe injuries or death.

The Four Rules of Gun Safety

In the words of Jeff Cooper, one of the world’s most accomplished firearms experts, the principles of gun safety are simple but extremely important. These principles are distilled into four simply-worded rules, and their purpose is to protect yourself, other shooters, and bystanders from the dangers of firearm misuse.

1: All guns are always loaded / Treat every firearm as if it is loaded

Of course, not all guns are technically loaded all the time, but the intention is to drill people into treating them as if they are for the sake of safety. Unless you have personally and actively verified that a firearm in your hands is indeed unloaded, treat it as if it is loaded and follow all other rules. Even if someone else hands you a firearm assuring you that it is unloaded, you should always check and verify it yourself.

2: Never point the muzzle at anything you are not willing to destroy

This fairly self-explanatory rule explains the concept of muzzle discipline, outlining the importance of not pointing guns at people, animals, property, or anything else you don’t intend to shoot.

3: Keep your finger off the trigger until you are ready to shoot

This rule explains the concept of trigger discipline. You should not allow your finger to rest on the trigger, intentionally or not, until and unless you have the full intention and readiness to shoot something. This rule also illustrates the importance of redundant gun safety measures. At best, sloppy trigger discipline results in a negligent discharge. At worst, you risk injuring or killing yourself and others.

4: Be sure of your target and what’s beyond it

This rule outlines two different concepts: the importance of target identification and knowing what may lie behind the target. Positive target identification is about ensuring the target is visible and identifiable. You may have heard the sentence “Don’t shoot at a sound,” many hunting accidents are the result of hunters breaking this rule, shooting at a fellow hunter believing it was a deer. The second concept outlines the importance of knowing what’s behind the target, and it is critical in every shooting scenario, from the range to the self-defense situation. The possibility of missing your target or passing clean through and continuing its path is always present. Because of this, you must be 100% sure the projectile will hit a safe backstop and not endanger anybody. Never assume that an interior wall will stop a bullet. The most common types of drywall and sheetrock in the United States will not reliably stop bullets or shotgun projectiles.

Additional safety considerations

Although the Four Rules of Gun Safety should cover your bases, they do not address every possible situation. Here are additional safety measures you should keep in mind when handling or shooting firearms:

  • Do not rely on your gun’s safety mechanism. Just because you engaged the safety doesn’t make it acceptable to break the Four Rules.
  • Always use the correct ammunition for your firearm.
  • Wear appropriate eye and hearing protection whenever possible.
  • Learn the basic operation and essential mechanical characteristics of your guns. The only way to safely handle a firearm is to understand how it works.

Firearms and Ammunition

Types Of Firearms

One can categorize firearms in myriads of ways; size, mechanism, design, intended purpose, type and power of ammunition fired, and many more criteria. There are three broad firearm categories: handguns, rifles, and shotguns. On occasion, you may see the term “long guns” used to group rifles and shotguns into a single category.


A handgun is a small firearm designed for one-handed use. Most handguns possess a relatively short barrel and lack a shoulder stock. Handguns are among the most commonly owned firearms. According to the ATF, gun manufacturers produced over 3.6 million handguns in the United States in 2019. Although handguns are popular with civilians, they also remain the firearm of choice for criminals. They are small, compact, and relatively inexpensive, making them desirable for violent crime. According to the FBI’s 2018 homicide statistics, of the 10,265 murders committed with a firearm in 2018, approximately 64% involved a handgun. Almost all handguns fall into one of two major categories: pistols and revolvers.


The pistol is the handgun of choice for today’s civilians, law enforcement, and military worldwide. The vast majority of pistols are semi-automatic (one shot per trigger pull). A typical pistol feeds from a detachable box magazine and features a reciprocating slide mounted on a frame made of steel, aluminum, or polymer. The slide houses the barrel and contains a firing pin, an extractor, a guide rod, and at least one recoil spring. The frame may possess additional controls, such as a slide lock lever, a manual safety lever, or passive safeties such as trigger or grip safeties. Loading a typical pistol requires inserting ammunition into the magazine, inserting the magazine into the firearm, pulling the slide back, then letting a cartridge go to the chamber. When a shooter fires a pistol, the recoil energy opens the slide, ejecting the spent case and compressing the recoil spring. After reaching maximum compression, the recoil spring releases its energy, closing the slide and chambering the next round. This process is called reciprocation. Upon firing the last shot, the slide usually remains locked open, serving as a visual indicator that the pistol is out of ammunition. Reloading from this point is a simple process. Remove the magazine, replace it with a loaded one, and press the slide lock release or pull on the slide to chamber a new round. Your pistol is now ready to fire again.


Although the semi-automatic pistol has existed since 1891, it was primarily a military sidearm until the 1980s, when it finally gained widespread acceptance among civilians and law enforcement. Before then, the revolver was the quintessential American handgun, and it remains a popular and viable alternative to pistols even today. A typical revolver consists of a frame, a barrel, a grip, a hammer (which either actuates a firing pin or directly serves as one), and a revolving cylinder with multiple chambers, one for each round. Most cylinders hold 5 or 6 rounds, although specific models may accept more. Most revolvers are either single-action (SA) or double-action (DA). These terms refer to the number of actions the revolver trigger can perform. On a single-action revolver, the trigger’s only purpose is to drop the hammer and fire. The shooter must manually cock the hammer before each shot. On a double-action revolver, the trigger cocks then drops the hammer in a single motion, eliminating the need to manually cock the hammer before each shot. The loading and unloading process of a revolver depends on its mechanism. SA revolvers typically feature a fixed cylinder and a loading gate, requiring the shooter to insert a cartridge into each chamber, manually rotating the cylinder until fully loaded. Once the SA revolver runs empty, the shooter must open the loading gate and use the spring-loaded ejector to eject each spent casing out of the gun. DA revolvers possess a cylinder release lever, allowing the cylinder to swing open to the side and giving the shooter access to all chambers at once. After firing every round, the shooter may open the action again, press on the ejector rod protruding from the top of the cylinder, and push the spent casings out. A double-action revolver with an exposed hammer still allows you to manually cock it and treat it like a single-action. Such models are called DA/SA revolvers, as they can essentially function in either mode at the shooter’s convenience. Setting a DA/SA revolver to single-action results in a much lighter trigger pull than in double-action mode, as the trigger’s only function then is just to drop the hammer.


A rifle is a long gun intended for two-handed use, typically featuring a shoulder stock and a relatively long, rifled barrel. All rifles are designed to shoot bullets like handguns, and most frequently from rifle cartridges. Some rifles are compatible with handgun ammunition. The rifle is the primary personal weapon of virtually every military unit worldwide, ever since the first muzzle-loaded rifled guns in the mid-19th century. Since then, firearms technology has evolved significantly, giving rise to a large array of different rifles. Civilians commonly use rifles for hunting, target shooting, and self-defense. Law enforcement units have increasingly adopted rifles to complement or replace rifles as tactical weapons. Criminals only rarely use rifles, as they are difficult to conceal effectively.


A shotgun is a long gun intended for two-handed use similar to a rifle but chambered for shotgun cartridges and intended to shoot shot pellets or slugs. Most shotguns possess a smoothbore (unrifled) barrel. Shotguns directly descend from the blunderbuss, a version of the musket (the predecessor to the rifle) designed to shoot multiple shot pellets instead of a singular projectile. Civilians enjoy using shotguns for hunting, self-defense, and various shooting sports (e.g., clay shooting). Law enforcement, particularly in the United States, use shotguns as a tactical weapon due to their versatility and the availability of less-lethal ammunition. Although shotguns possess an extensive military history, they are now considered a special-purpose weapon, used only in specific circumstances, such as door-breaching or close-quarters combat. They are also rarely used by criminals, as they are just as challenging to conceal effectively as rifles.

Long gun mechanisms

There are many ways to categorize the operating mechanism of long guns. The two broadest categories of rifles are single-shots and repeating firearms. Single-shots feature simple mechanisms, consisting of little more than an action, a barrel, a stock, and a trigger. Some variants possess multiple barrels (e.g., double-barrel shotguns) but functionally rely on the same basic principle. The vast majority of rifles today are repeating rifles (also called repeaters). A repeater is a single-barreled firearm capable of holding more than one round, typically through the use of some type of magazine (or similar feeding system). Within this category, you will find two sub-categories: manual repeaters and self-loaders. A manual repeater is a rifle with a manually operated mechanism for loading and unloading rounds. Typical manual repeating actions include bolt-actions, lever-actions, and pump-actions. A self-loading rifle is a rifle capable of automatically chambering a fresh round between each trigger pull, harnessing part of the recoil energy generated by a fired shot to send the bolt rearward and eject the spent casing. Like semi-automatic pistols, self-loading rifles usually possess a recoil spring to bring the bolt back forward, chambering the next round in the process. Self-loading rifles include semi-automatic rifles, fully-automatic rifles, burst-fire, and selective-fire rifles (e.g., submachine guns, assault rifles, machine guns, etc.)


A bolt-action firearm is a repeater requiring the shooter to manually operate the bolt to extract spent casings and chamber the next round. Bolt-action rifles usually feature rotating bolts, requiring the shooter to turn the bolt to lock and unlock it. Some are straight-pull bolts, which eliminate the need to turn the bolt, merely requiring a straight pulling or pushing action. Most bolt-action rifles feature fixed, internal magazines, although specific models are compatible with detachable box magazines. Most deer hunting rifles and most sniper rifles are bolt-action firearms. Such rifles typically feature scopes instead of iron sights for long-distance precision shooting.


A lever-action firearm is a repeater featuring a rotating cocking lever, usually incorporated around the trigger guard. Like bolt-action rifles, most lever-actions feature fixed, internal magazines. Usually, these magazines are tubular and mounted under the barrel. Most cowboy-era rifles were lever-actions, such as the famous Winchester Model 1873. Although lever-actions are considered obsolete, they remain popular among civilian shooters in the United States, and they are still in production today.


A pump-action firearm (sometimes also called slide-action) is a repeater featuring a horizontal slide, usually mounted under the barrel. Although most pump-action firearms found today are shotguns, the mechanism first appeared on rifles such as the Colt Lightning Carbine, first produced in 1884. Operating the slide is relatively simple: the shooter opens the action by pulling the slide rearward, closing it by pushing it back forward. The motion is reminiscent of using a pump, hence the term “pump-action.”


A semi-automatic firearm is a self-loader allowing for one shot per trigger pull. In other words, you can shoot a semi-automatic as quickly as you can pull the trigger. Most semi-automatic rifles accept detachable box magazines, whereas most semi-automatic shotguns have retained internal tubular magazines. The most popular type of semi-automatic firearm in the United States today is the modern sporting rifle or MSR. An MSR is a rifle resembling a military rifle, with identical controls and most of the same features. The AR-15 is a type of MSR based on the M16 rifle, and AR-15 type rifles are the most common MSRs.

Fully automatic, burst-fire, and selective-fire

A fully automatic firearm is a self-loading gun capable of firing continuously, repeatedly discharging ammunition for as long as you pull the trigger. A burst-fire firearm can discharge multiple rounds per trigger pull like a full-auto, but it features a mechanism limiting the number of shots per trigger pull to 2, 3, or 4. A selective-fire (or select-fire) firearm possesses a fire selector lever, which often doubles as a safety lever. Most select-fire guns have a safe mode, a semi-automatic mode, and either a burst-fire mode, an automatic fire (full-auto) mode, or both. Typical firearms in this category include submachine guns, assault rifles, and machine guns. These firearms are typically reserved for military or law enforcement use only and are generally not accessible to civilians. In the United States, the National Firearms Act regulates the civilian ownership of such firearms.

Types Of Ammunition

Firearm ammunition exists in many different sizes and types, with a wide selection of projectile types. A typical ammo box should provide you with the following information: Caliber or gauge, projectile weight, bullet or projectile type, muzzle velocity, and muzzle energy.

Caliber and gauge

The caliber or gauge of a cartridge doesn’t just tell the shooter about its dimensions; it indicates which firearms can safely fire this ammunition. In pistol and rifle ammunition, caliber notation may either be metric or imperial. An example of a metric caliber notation is 5.56x45mm. The first number (5.56) denotes the diameter of the bullet in millimeters, whereas the second number (45) denotes the length of the casing. An example of an imperial designation is .45 ACP. The number (.45) denotes the bullet diameter in inches, followed by a specific name or letters intended to separate it from other cartridges with a similar diameter (e.g., .45 ACP vs. .45 Colt). A smaller number represents a small caliber, whereas a larger number represents a larger caliber. Typical shotgun ammunition uses neither metric or imperial, using gauges instead. The gauge number is inversely proportional to the bore diameter. In other words, the smaller the gauge, the bigger the diameter. The only exception to this rule is the .410 bore, which uses imperial notation. Ammo calibers may be categorized into five major groups, based on the firearm types intended to shoot them: pistol, revolver, rifle, shotgun, and rimfire. Examples:

  • Pistol: 9x19mm Luger, .40 S&W, .45 ACP
  • Revolver: .38 Special, .357 Magnum, .44 Magnum
  • Rifle: 5.56x45mm, 7.62x39mm, .308 Winchester, .30-06 Springfield
  • Shotgun: 12 gauge, 20 gauge, 28 gauge, .410 bore
  • Rimfire: .22 Long Rifle, .17 HMR, .22 WMR

Projectile weight

Most pistol and rifle ammo boxes specify the number of grains each bullet weighs, whereas shotgun shell boxes usually specify a payload in ounces. A grain is equal to 1/7000 of a pound. The higher the grainage, the heavier the bullet. Although the weight of a projectile impacts its performance, it is generally only relevant at extended distances. There is no specific advantage or disadvantage to using light or heavy bullets.

Projectile type

In pistol and rifle ammunition, the bullet type is represented by a three- or four-letter code, which gives you an idea of the shape and construction of the bullet. Examples of the most common abbreviations:

  • FMJ: Full Metal Jacketed. Bullet with a lead core and a copper or nickel jacket. Best suited for target shooting or training.
  • JHP: Jacketed Hollow Point. Bullet with a hollow cavity designed to expand upon impact. Best suited for personal defense.
  • JSP: Jacketed Soft Point. Similar to an FMJ but with an exposed lead tip, designed to expand, though less dramatically than a JHP. Best suited for hunting.
  • LRN: Lead Round Nose. 100% lead bullet with no jacket. Best suited for target shooting or training.
  • LSWC: Lead Semi Wadcutter. A specially-shaped 100% lead bullet designed to punch perfect circular holes into paper and cardboard targets. Best suited for target and competition shooting.

In shotgun ammunition, boxes of birdshot and buckshot shells feature a number code instead, representing the diameter of each pellet. Birdshot usually ranges from #9 (0.08”) to BB (0.18”), whereas buckshot typically ranges from #4 (0.24”) to #000 (0.36”). The larger the shot size, the fewer pellets in each shell. Slug shell boxes generally state the projectile type in plain letters (e.g., rifled lead slug), with no letter or number codes.

Muzzle velocity and energy

The muzzle velocity is a notation expressed in either feet per second (ft/s or fps) or meters per second (m/s). It indicates the speed at which the projectiles will leave the barrel of a typical firearm. The muzzle energy is a notation expressed in either foot-pounds force (ft-lbf) or Joules (J), indicating the amount of kinetic energy carried by the projectile as it leaves the muzzle. Note that the longer the projectile travels past the barrel, the more velocity (and therefore, energy) it will lose over time.

In Sum

At IFA Tactical, our mission is to educate Americans about gun rights, gun safety, and the Second Amendment. We carry a large selection of pistols, revolvers, shotguns, and rifles to help you exercise your Second Amendment rights. We also offer many useful gun services, from Cerakote gun paints to gunsmithing. Browse our online inventory from the comfort of your home. If you have any questions or requests, call us at (586) 275-2176. We are always ready to answer your questions and help you find what you need.

Call Now Button