A Primer on the 5 Parts of a Gun – The Semi-Automatic Pistol

One of the key concepts of gun ownership is the ability to maintain your gun in top operating condition. This concept requires at least a basic understanding of the parts of a gun, how they work together, and what problems can occur if they aren’t properly maintained. A competent gun owner knows the names and functions of the different parts of the gun, and can readily explain them to others.

All guns share some common characteristics, such as having a barrel and a trigger. Much past this point in describing the parts of a gun, the various configurations and designs diverge. The differences are enough that each style and design of a gun requires considering them separately when describing the different parts. For this article, we will look at the semi-automatic pistol as our example, since it is a classic concealed carry weapon.

The Semi-Automatic Pistol – A Primer on the Parts of a Gun

The semi-automatic pistol is probably the most widely chosen style of handgun selected by concealed carry license holders. There are many reasons for this choice but most handgun owners who concealed carry go to the magazine capacity of these pistols. In general, revolvers carry five or six rounds of ammunition in the chamber. In comparison, a medium-framed semi-automatic pistol that can be easily concealed by most people can carry 10 to 15 rounds of ammunition in the magazine.

Whatever your reasons for choosing the pistol that you carry every day, it is in your best interest to know and understand the functions of the different parts of a gun. Being familiar with your gun and being able to describe a problem in words that other gun owners and gunsmiths understand is critical to keeping your firearm functioning in top condition.

How does a Semi-Automatic Pistol Work?

In truth, your semi-automatic pistol is a piece of precision engineering and manufacturing. To function reliably, the tolerances and clearances of the parts of a gun must be within fractions of an inch. These close tolerances make the care and maintenance of these parts essential to ensure that they continue to work together.

Unlike a revolver, in which the cylinder both holds the ammunition and acts as the firing chamber, the semi-automatic pistol uses an integrated chamber and barrel design. The parts of a gun work together in unison to fire a bullet.

  • The action of pulling the slide back and releasing it pulls a cartridge from the magazine into the chamber, where it usually is carried, ready to fire.
  • Pulling the trigger causes the firing pin or striker to come forward, striking the primer in the cartridge and the gun fires. 
  • The recoil from the fired cartridge drives the slide backward. The ejector pulls the spent cartridge from the chamber and ejects it from the pistol. 
  • As the slide returns forward, a fresh cartridge is taken from the magazine and inserted into the chamber, ready to be fired.

As you can see, to describe those simple steps required using terminology with which most owners of semi-automatic pistols are familiar. However, many don’t grasp the proper terminology and have trouble grasping the way the parts of a gun function together when the gun fires.

The Parts of a Gun in Question – A Pistol Owners Reference

In general, when we refer to the parts of a gun, there are three basic sets of components. The three groups of parts are:

  • The action – The action refers to the collection of parts that work together to make the gun operate. These can include the trigger, the hammer or striker, the firing pin, and so on.
  • The stock or grip – The stock or grip is the thing you hang onto when you fire the gun. In rifles, the stock is the platform that holds the other parts. On pistols and revolvers, the grips attach to the frame of the gun. The grips serve no other purpose but to serve to hold the gun in a good shooting grip.
  • The barrel – The barrel of your gun is nothing more than a metal tube bored to a precise diameter with lands and grooves to impart spin to the bullet as it travels down the barrel. In shotguns, this metal tube has no lands and grooves and presents a smooth surface for the shot to travel.

A semi-automatic pistol is no exception. Now let’s look at the parts of a gun that make up the action of a semi-automatic pistol and how they function and work together.

The Frame

If you take every other component of the semi-automatic pistol from the gun, you have the frame of the pistol. The frame is the part of a gun that acts as the foundation and support system for every other functioning part. Pistol frames can be machined metal or, in some newer lightweight pistols, a polymer compound.

The frame will have the rails or grooves in which the slide assembly rides. The trigger guard is part of the frame as well. Also, the frame will have the necessary slots and holes machined in to provide the mounting positions for the functioning parts of the pistol.

Most gun owners will never have reason to disassemble their pistol to the bare frame. Manufacturers of modern semi-automatic pistols design them such that you can clean and lubricate your pistol without resorting to a complete disassembly to the bare frame. I suggest that if your pistol requires a repair that necessitates a complete disassembly that you take your pistol to a competent gunsmith. That being said, understanding the parts of a gun will still help you speak that language and triage if needed.

The Barrel

Your semi-automatic pistol uses a barrel machined from high strength steel. The parts of a gun that relate to the barrel most are: 

  • The Breach – The breach is one of the parts of a gun found at the rear end of the barrel and contains the chamber. The cartridge inserts into the chamber.
  • The Bore – Once the cartridge fires, the bullet travels down the tube in the barrel called the bore. The bore has high spots and low spots in a spiral pattern. The high and low spots, called lands and grooves cause the bullet to spin which increases the stability of the bullet as it leaves the barrel of the gun.
  • The Muzzle – The bullet exits the bore from the muzzle. Most muzzles are smooth, with a slight rounding called a crown. Some pistol barrels may have a short length at the muzzle that has threads. These threads provide a place to attach a suppressor.

The Slide

The top portion of your semi-automatic pistol is called the slide. The slide rides on the top of the frame and is key to the functioning of the modern semi-automatic pistol. There are several vital components housed in the slide and they all are important parts of a gun.

Different manufacturers of pistols have different designs, which may include different parts. In general, the essential components found in the slide of most modern semi-automatic pistols include:

  • The barrel – I have already described the barrel and it’s parts of a gun. The barrel rides inside the slide on most semi-automatic pistols and may even pivot to facilitate the loading cartridges into the breach.
  • A recoil spring assembly – The recoil spring assembly can contain several different elements depending on the manufacturer and its design. Usually, the recoil string assembly has a recoil spring guide and the recoil spring.
  • An extractor assembly – The pistol must have a way to remove and discard the spent cartridge casing. The removal of the spent cartridge from the chamber is the job of the extractor assembly. While small and seemingly insignificant, this assembly is vital to the functioning of the pistol and is subject to wear and tear. If your pistol is having trouble functioning reliably, a worn ejector should be suspected.
  • The ejection port – The slide will have an opening machined into one side near the rear. This opening is where the extractor ejects the spent cartridges.

As you can see, there are many parts of a gun that can be broken into many other (smaller) parts. The slide will also have the front and rear sights mounted on top. In some instances, the sights may be integral to the slide and are not adjustable. Better semi-automatic pistols will feature adjustable sights and, in some cases, replaceable sights.

The Functioning Parts that Make it all Work Together

Inside the frame near the rear of the pistol reside several critical parts of a gun:

  • The trigger and trigger assembly – The trigger, that part that mechanically activates the firing mechanisms of your pistol, is part of a much more complex assembly that includes various parts, springs, and pins. Disassembly of the trigger components on a modern semi-automatic pistol is not something that we recommend average gun owners undertake. In some cases, disassembly and reassembly require special tools.
  • Safety assembly – Some semi-automatic pistols feature a manual safety. The safety of semi-automatic pistols operates in several ways. On some semi-automatic pistols, the safety or safeties are integral to the trigger mechanism and do not require the shooter to manipulate a safety bar or button. 
  • De-Cocker – If your semi-automatic pistol can fire double-action, it may have a decocker. The decocker allows you to reset the hammer to a safe position out of the fully cocked mode so that you can safely carry a cartridge in the chamber of the gun. 
  • Magazine release – One of the advantages of the semi-automatic pistol is the way cartridges are carried and fed to the pistol. The mechanism for this is the magazine. The magazine fits into the frame of the pistol through the bottom of the grip. Reloading requires a means to release the magazine from the frame of the pistol allowing a full magazine insertion quickly and efficiently.
  • Slide Release or take-down lever – Near the front of the frame ahead of the trigger guard, most semi-automatic pistols have a small level or slide that releases the slide from the frame. In some instances, to get the slide to disengage from the frame entirely, you must pull the trigger. Take every precaution to make sure that your pistol is unloaded and in a safe condition before performing this action. Remove the magazine, cycle the slide, and visually inspect the chamber of the barrel to ensure that the pistol is unloaded and in a safe condition.
  • Slide Lock – The slide lock is located near the rear of the frame. When the magazine is empty, most semi-automatic pistols will engage the slide lock to hold the slide in the rear position until a new magazine goes into the frame of the pistol. The slide lock lever disengages the slide if the pistol doesn’t do this when the new magazine is inserted. The slide lock used manually locks the slide open, a visual reference that the pistol is in a safe condition.


Technically, not a part of the pistol itself, the pistol just will not function as designed with a magazine filled with the proper cartridges for the pistol. That being said, the magazine is still an important element, and has its place among the parts of a gun.

  • The body – The body of the magazine is a metal or polymer square tube that fits tightly inside the magazine well of the pistol frame. 
  • Magazine spring – The magazine spring fits inside the magazine housing and provides the tension that keeps the cartridges loaded in the magazine tight at the top of the magazine where the pistol action can retrieve them during the firing sequence.
  • Spring follower – At the top of the magazine, spring is the spring follower. This small piece of metal or plastic designed to keep the cartridges in the magazine properly aligned as they travel up the magazine. 
  • Baseplate – At the bottom of the magazine body is the base plate. The baseplate keeps everything together and functions correctly. The base plate fits tightly into the magazine body providing support for the magazine spring. It is possible to disassemble magazines for cleaning by removing the base plate allowing removal of the magazine spring and follower. 

Putting the Parts of a Gun Together

Take each of these parts of a gun, put them together correctly, and you have a functioning semi-automatic pistol! Keep them clean, oiled, and maintained to have a pistol that operates reliably and shoots accurately. If you do have problems and need to consult a gunsmith, with an understanding of the parts of a gun and their names, you can easily describe the problem and find the proper solution. Happy shooting!