Basic Anatomy: Semi-Automatic Pistol


Today, we’re going to go over the basic pieces which, when combined, create a semi-automatic pistol. I’ll be using my personal Springfield XDm 9mm as an example. By the end of this post, you will be familiar with the nomenclature and operation of this firearm!

Let’s begin with the biggest pieces. Here we have the pistol field-stripped, that is, broken down as far as you would for regular maintenance. The 5 pieces you see highlighted here are, in order, the recoil spring, barrel, slide, frame, and a loaded magazine. I’ll give a quick description of each piece below.

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When the trigger is pulled and a round fires, the forces generated push the slide backwards, ejecting the spent case. This backwards motion also compresses the recoil spring, which sits underneath the barrel when the handgun is assembled. The job of the recoil spring is to snap the slide forward again into the closed position, chambering a new round and holding the slide closed (as you see in the top picture).


The barrel is what the bullet travels down after being fired, giving it direction and imparting spin on the projectile to stabilize it in flight. The front of the barrel (which is also the front of the firearm) is called the muzzle, and the back is called the chamber. There’s a lot more that goes on inside a barrel, but we’ll cover that in a later Advanced Anatomy post.


The slide is where the magic happens. Seriously, most of the moving parts and all of the explosive forces are generated and contained in the slide. You’ll notice that’s why we have polymer (plastic) framed pistols, and not polymer slide pistols. The slide needs to be strong enough to repeatedly withstand all that action. The recoil spring and barrel both reside inside this piece, as does the firing assembly (which I’ll cover in Advanced Anatomy).


This is the piece you grip, and on my Springfield, it’s made of polymer to save weight. The frame also contains a wealth of different levers and doo-dads, which we’ll cover in just a moment. The slide rides along the top of the frame, and magazines fit inside.


Magazines (or mags) are a container for the firearm’s cartridges (bullets). Every firearm has a different magazine capacity, and that’s due to different sized bullets (calibers), as well as engineering design to be slimmer, longer, taller, etc. They slide into the frame, like so:BMM_9503

The mags for my XDm fit 13 9mm rounds. There are also magazines that increase the capacity to 19! That’s a lot of firepower! Here you can also see the slide locked back, and that’s the barrel poking out of the front at an angle. At an angle? Shouldn’t it be straight!? Yes, it’s supposed to do that! When the slide moves back, the barrel drops down so the next round more easily slides into it. The barrel locks back into a dead straight position when the slide moves forward.

There are just a few extra pieces on the slide I want to cover before we move on to the frame, the sights and the ejection port.

Sights HighlightThese are what you use to aim the barrel at your target. At the back of the firearm sits the rear sight, and above the muzzle is the front sight. This is what they look like from the shooter’s point of view:Sight AlignmentWe’ll talk all about how these two sights work, how to use them, some of the different styles available, and a host of other topics once we start going over firing a handgun. For now, just know that these are what you use to aim the weapon.


Ejection Port Highlight

Okay, the ejection port isn’t a piece so much as a lack of one. It’s the cutout in the middle of the slide where the spent cases are flung from the firearm. I mention the ejection port because it’s very important not to block it while you’re shooting. Hot brass gets spit out of here, and if the port gets blocked for any reason, the firearm will jam. This is bad. You can see what it looks like when open in the magazine section above.

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Now let’s talk about the levers and doo-dads I mentioned before.These are all things that you will regularly manipulate when handling your firearm, so they’re important to be familiar with!


This is where your hand goes. A good grip is critical to your shooting success, and manufacturers know this, so they spend a lot of time and effort designing ergonomic grips. All of the textures and patterns you see on this grip are designed to give you added traction while you’re holding the firearm. Grips on most pistols have pieces on them that can be swapped with larger or smaller variants to create a custom grip; this Springfield has “replaceable backstraps”. The backstrap is the bottom rear piece of the grip (It’s next to the XDm logo in the picture), and can be removed and swapped for one of a different size. This allows you to tailor the grip to the size of your hand. Also worth noting is that the firearm is designed so that you can reach and manipulate all of the doo-dads (save the disassembly lever) without changing your grip on the weapon.


A gun isn’t a gun without a trigger. This piece of the weapon is arguably the piece that you’ll become the most intimate with. Triggers come in many variants, and could almost be said to have their own personalities, as you’ll hear them described as creepy, light, heavy, fragile, slick, good, gorgeous, horrendous, and other adjectives as well! The trigger is where you interface with the weapon in order to fire it. Many triggers can be adjusted for weight, which is the measurement of how much pressure it takes to pull back the trigger to the point that it fires a shot.


The trigger guard is the section of material that shrouds the trigger. It’s there to block anything from accidentally pulling the trigger, so in a sense, it’s a passive safety that’s always engaged. You won’t find a firearm nowadays without one.


These are critical. A firearm’s safeties are there to ensure that the gun only fires when you want it to. They are insanely important, and should NEVER be tampered with. There are a few different types (and I’ll give safeties their own post later on), but let’s go over the two that my XDm uses. On the trigger, you’ll see a small lever protruding from the front; this is called the trigger safety, and unless the lever is depressed by your finger resting properly upon it, the trigger won’t move, so the weapon can’t fire.

The other safety is a lever located on the back of the grip, above the backstrap, and is aptly named the grip safety. It operates on the same premise as the trigger safety (as a matter of note, both of these safeties fall under the “grip safety” category, because they operate by ensuring that you’re properly gripping the handgun). Unless the lever is depressed into the grip, the trigger cannot engage the rest of the firing assembly to set off a shot. These two safeties work in tandem, that is, both of them must be disengaged in order for the handgun to fire. These differ from “active safeties”, which are switches that manually toggle from safe to fire.

I cannot stress enough that handgun safeties do not make a handgun more or less safe! The engineered safeties are only there to help you prevent accidents. What makes a firearm truly safe is the training and knowledge of the person wielding it, therefore, train until YOU are safe and responsible with your guns.


The magazine release is simply a button that lets go of the magazine, allowing it to drop from the firearm. Some mag releases are ambidextrous, which means they can be activated from either side of the firearm. Pretty simple stuff.


This lever can be pushed up to lock the slide in the rear position, like in the magazine picture near the top of the post. The handgun is engineered to automatically do this when the last round is fired and the magazine is empty. You can push down on the lever to allow the slide to snap forward.


When it comes time to clean your firearm, you’ll need to take it apart, or “field strip” it. The disassembly lever allows you to do that by pivoting a small catch out of the way of the slide so that the whole piece can then be slid off the front of the frame. The lever will not actuate unless the slide is locked back, and the gun will not fire with it in the disassembly position.

This concludes basic semi-automatic pistol anatomy! You should now be familiar with most of the parts of these types of firearms and their operation. Keep in mind that they’ll look different from weapon to weapon, but they’ll always be there, and their purpose is always the same.

Until next time, have fun, be safe, and shoot straight!


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