Shotgun Shell Sizes and Why You Need to Know About Them

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Last Updated on July 8, 2021.

Writer for Minuteman Review, handgun aficionado and artisan firearms reviewer. 

Whether you own a shotgun or intend to buy one, understanding the different shotgun shell sizes — gauges and lengths in particular — is essential. This knowledge will allow you to shoot safely and effectively. 


Shotgun Ammunition

You’ve probably seen references to different shotgun shell sizes — 12 gauge, 20 gauge, 2¾”, 3”, etc. What do these designations indicate, and why is this important? Firing shotgun shells of the incorrect gauge or length can be hazardous to both your gun and your safety.   

Part of being a responsible gun owner is understanding how your shotgun functions and using the proper ammunition. 


Shotgun Shell Sizes

Shotgun shells are composed of the following components/parts:

Base

The base is the cartridge case head that contains the primer pocket, flash hole, and rim for headspacing and extraction. The base, which is usually made from brass, extends upward, forming a collar that supports the case.

Case

The case holds the propellant charge, projectile or projectiles, and wadding. Originally made from thick paper and then brass, the modern shotgun shell case is plastic.

Primer

A cylindrical metallic cup, resembling a button, which contains a primary explosive, the primer serves the same purpose in a shotgun shell that it does in a handgun or rifle cartridge. When struck by the firing pin, the priming compound detonates, igniting the propellant charge through the flash hold in the base.

Shotgun Boot Camp How to Load Your Shotgun

Propellant

Also called gunpowder, the propellant charge burns when ignited by the primer. This combustion produces high-pressure expanding gases, which drive the ammunition through the barrel and toward the target.

Wadding

Wadding acts as a spacer between the burning propellant and the shot pellets, allowing for even distribution of force to the shot charge. It also keeps them from becoming deformed during the acceleration process.

Shot

“Shot” refers, collectively, to spherical lead, steel, or tungsten projectiles, which are individually called “pellets.” Shot pellets are further divided into birdshot and buckshot.

Birdshot pellets are typically tiny, and the weight of the charge is measured in ounces. These pellets allow the shotgunner to hit game animals, such as birds, and sporting targets that move at high velocity.

Buckshot pellets are larger and more penetrative. Buckshot is used for hunting large game and self-defense.

You may check our recent article about shotgun shot size to understand better this topic.

Slug

In shotgun shells that do not contain shot pellets, the non-exotic alternative is the slug. Shotgun slugs are akin to heavy, blunt-nosed rifle bullets and deliver more penetrating power and energy to the target at greater ranges.

There are two types of slugs: rifled and sabot. Rifled slugs, such as the Foster and Brenneke, are solid, full-caliber projectiles designed to be fired in smoothbore barrels.

Sabot slugs are sub-caliber projectiles enclosed in discarding plastic sleeves and are designed to be fired in rifled shotgun barrels.

What is Gauge?

One of the first points of confusion regarding shotgun barrels and shells is the term “gauge.” 

Handgun and rifle calibers are expressed in hundredths or thousandths of an inch (e.g., .45 caliber, .223 caliber) or millimeters (e.g., 9mm, 5.56mm). Shotgun calibers, however, are typically expressed in terms of “gauge.”

In the context of shotguns, “gauge” refers to the diameter of the bore. This is an archaic system of measurement that refers to the number of lead balls of a particular diameter it takes to equal one pound. 

For example, in a 10-gauge shotgun, which has a bore of approximately .775”, it would take ten lead balls of this diameter to equal one pound. In a 12-gauge shotgun, 12 lead balls of .729” would be required, and so on. 

In handgun and rifle calibers, the lower the number, the smaller the bore diameter. Shotguns are the opposite — the lower the gauge number, the larger the bore diameter

One of the few exceptions to this rule is .410 bore, a shotgun caliber measured in thousandths of an inch and equivalent to about 67 gauge. 

Shotgun Shell Length

Following the caliber or gauge of the shotgun is the length of the shotgun’s chamber and, thus, the appropriate shell length. For example, the standard length for a 12-gauge shotgun’s chamber is 2¾”. 

If you buy a packet of 2¾” shotgun shells, you may notice that the shells fall short of this number. That’s because the length of the chamber corresponds to the length of a fired shotgun shell

Why This Matters

Shotgun shell sizes matter for a variety of reasons. First, if the chamber of your shotgun is 2¾” long, you shouldn’t fire 3” magnum rounds in it. 

If you’ve fired shotguns before, you may have found that a 3” shotgun shell will fit into a 2¾” chamber. You may have even fired one or two without incident. So why is this a problem? 

Plastic shotgun shells have a crimped opening. When you fire a shotgun, the expanding gases generated by the burning propellant force the wadding and shot charge forward, opening the shotshell and extending its length

As the shotgun shell headspaces on the rim of the case head (base), there’s a space immediately in front of the shell inside the chamber that it can unfold into. Ahead of the shotgun chamber is the forcing cone, which tapers toward the barrel diameter. This is not that dissimilar from the forcing cone in a revolver — it guides the ammunition into the bore. 

Shotgun Boot Camp Shotgun Types

A 3” shotgun shell is not 3” in length until it’s fired. As a result, you can chamber a 3” shotgun shell in a shorter chamber. If you attempt to fire a 3” shotgun shell in a chamber designed for a 2¾” shell, however, the crimp will unfold into the forcing cone

As the forcing cone is tapered, the crimp will not unfold at the same diameter as the chamber, constricting the shot charge and increasing the chamber pressure

Shotgun shells of this length also hold more powder and more shot. If the shotgun’s receiver is not rated for 3” shells, this can be dangerous. 

The effects of this can be unpredictable, but you risk damaging the gun and potentially injuring yourself. 

Aside from safety, the reason that the length of the shotgun shell matters is that it affects your preferred type of shooting. The longer the shotgun shell, the heavier the payload it can carry. More shot pellets can increase the effective range, shot pattern density, and lethality of your shotgun. 

See Related Article: Understanding Shotgun Shells


Magazine Capacity

However, you can safely and effectively fire shotgun shells that are shorter than the chamber. In a 2¾” chamber, for example, you can fire 2½” shells. So-called mini shells can be beneficial for short-barreled shotguns with correspondingly short magazine tubes. 

Most pump-action and semi-automatic shotguns are fed from tubular magazines that are parallel to and below the barrel. In these magazine tubes, the shotgun shells are loaded one in front of the other. 

The exact capacity of the magazine tube depends on the length of the shotgun shells you insert. Using shorter shells can increase the effective capacity from five rounds to as many as eight without the need for modification. 

Longer shotgun shells take up more space in the magazine tube, reducing the capacity. When you’re searching for the best shotgun shell sizTes for your gun, keep the capacity in mind. 


In Sum

Understanding shotgun ammunition will improve your safety and effectiveness as a shotgunner. There are a variety of shotgun shell sizes to choose from, depending on your shooting style.