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Gun Components

In 99.9% of all cases, all guns include the following parts: muzzle, breach, hammer and trigger. These components often determine how a firearm operates and how it is classified.

Muzzle: The Business End of a Gun

Muzzle = Front. Or, more specifically, the muzzle is the opening on the front of a firearm. This is where the projectile comes out of. Click on the examples below for more detail.


The Breech

Simply, the breech is the back. With early firearms, the technology limited how guns were loaded. For centuries, guns could only be loaded through the muzzle and they were known as “muzzle-loading” guns. Later, as technology improved, guns could be loaded through the breach and were referred to as “breech-loading”. Click below to see some examples of gun breeches:


The Hammer

The hammer is the part of the firearm that makes contact with the bullet primer to ignite the powder and propel the bullet out of the muzzle (read more about bullet cartridges). For most handguns and some rifles, the hammer is visible on the outside of the firearm. However, for most rifles and shotguns and some pistols, the hammer is internal.

With some guns, the hammer doesn’t even contact the primer directly at all. In those cases, a firing pin is used. The firing pin is struck by the hammer driving it forward into the bullet’s primer to fire the round.


The Trigger

The trigger is the part of a firearm that files the round. On certain guns, like single action revolvers, the hammer has to be “cocked” – or pulled back into position – before the trigger can be pulled. In those cases, the pull of the trigger releases the hammer to fire the round. With most other guns, the trigger pull is considered double action in that pulling the trigger both cocks the hammer and releases it thereby firing the gun..



The Bullet Cartridge


The method of using three separate components (projectile, powder & charge) to fire projectiles continued for hundreds of years until the late 19th century when the first firearm “cartridge” was introduced.


click to enlarge

The cartridge was a leap forward in firearm design in that, for the first time the projectile, powder and charge were all contained in one single piece. Often mistakenly referred to as a “bullet”, cartridges use metal casings (usually made of brass) to contain the projectile, the powder and the percussion cap in one weatherproof container. Thus was born the modern bullet cartridge consisting of four components:

  1. the case or shell (the exterior holding everything together)

  2. the projectile (bullet)

  3. the powder (black powder replaced later by smokeless black powder)

  4. the primer (replacing the percussion cap used to create the spark)

Slug vs. Shot

While all cartridges are made up of the same four basic components of case, projectile, powder & charge, there are two primarily different types of cartridges used today with the projectile and case being the elements that define each. Most ammo cartridges contain a single projectile, often referred to as a “slug” or a “bullet”. However, there is a second type of cartridge that fires multiple projectiles which are referred to as “shot”. This, as you can imagine, is where a “shotgun” gets it’s name.

Typical bullet cartridges (also referred to as rounds) are designed for hitting a single target with accuracy being the primary goal. The majority of firearms including pistols, rifles and machine guns all use these types of rounds. Bullets are measured by their physical size which is referred to as “caliber”.

Shot cartridges are often referred to as “shells” or “shotgun shells” and typically contain multiple projectiles with the purpose of spreading the shot over a wide area. The primary purpose for this is hunting where a moving target is often difficult to hit with a single projectile. In most cases today, shotgun shells are made of plastic with a brass backing containing the primer.

Shotgun shells are measured in “gauge”, which is the weight, in fractions of a pound, of a pure lead round ball that is the same diameter as the internal diameter of the barrel. So, a shotgun is called 12 gauge because a lead sphere that just fits the inside diameter of the barrel weighs 1⁄12 of a pound.

What is Caliber? Bullet Sizes Explained


You’ve heard it on your favorite cop show, “looks like the killer used a twenty-two,” or, “he was killed with a nine millimeter.” But, if you’re curious like I was, you’re asking yourself, “what the heck is a twenty-two and what does it mean anyway?”

Well, common sense would suggest that the numbers have something to do with size and that is exactly correct. When you hear various numbers being mentioned related to bullets, the number being referred to is what’s called the bullet’s “caliber”. Caliber is a unit of measurement related to a bullet’s size. Specifically, what’s being described is the bullet’s diameter.

To be even more specific, the caliber of a bullet is the measurement of the diameter of the slug (or projectile) part of the bullet cartridge. This is important because in some situations, the bullet casing will be wider than the slug itself. But the caliber is specifically describing the width of the slug portion. Caliber does not refer to the length or power of the bullet (in most cases), but simply the diameter of the bullet.

The Bottom Line: The Width of a Bullet Determine’s Its Caliber


I know, you’re thinking, “but what’s a twenty-two compared to a nine millimeter?” Well, as with all measurements, there’s the American way and the Metric way of measuring. The metric is simple, a nine millimeter (9mm) is 9mm in diameter. The American measurement is a little different. A twenty-two (or 0.22) is twenty-two one hundredths (22/100’s) of an inch in diameter – or a little less than a quarter of an inch. Similarly, a 0.44 is 44/100’s of an inch, a .50 caliber is a half inch, and so on.

Firearms 101

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