A Shotgun Caliber Guide: An Intro Into Ammo And Its Functionality

Shotguns are some of the most versatile weapons in the world. The key to this versatility is their ammo types and what these ammo types deliver. A 12 gauge shotgun caliber can be used to kill animals as small as birds and as big as bears. They are effective home defense weapons and can engage a target as close as one foot and far away as 100 yards. Everything a shotgun can do is dependent on the ammo loaded into it. 

Unfortunately, a lot of versatility means a lot of different ammo types which can be confusing. Today we are putting together a shotgun ammo guide to demystify shotgun calibers.


Shotguns are the only small arm I know measured in gauges. A gauge is a very old way to measure the inside of the bore. The gauge of a shotgun caliber is determined by the number of solid spheres of lead that will fit down the bore of the weapon. The number that measures the gauge is derived from how many lead spheres of that size it will take to equal a pound. If I took a pound of lead and divided it into 12 equally sized spheres those would be 12 gauge spheres. It’s odd and not important to know, but I wanted to share.

What is important to know is that the smaller the number the larger the shotgun is. So a 20 gauge is smaller than a 12 gauge. A 10 gauge is bigger than a 12 gauge. 

To make things even more confusing there is a single shotgun caliber measured in inches and that’s .410. There are lots of shotgun calibers out there, but the three most common are 12 gauge, 20 gauge, and .410. 

Slightly uncommon calibers include 28 gauge, 16 gauge, and 10 gauge. Rare calibers include 8 and 4 gauge which isn’t a concern. For home defense and hunting 20 and 12 gauge tend to be the preeminent calibers with .410 lagging slightly behind.

Shell Length 

Shotgun shells come in a variety of different lengths and they will often depend on the caliber of the shotgun shell. The longer the shell the more shot it is capable of holding, but bigger shells offer more recoil. Your shotgun will determine if the length of shell you can use. As we’ve established the three most common shotgun shells are 12 gauge, 20 gauge, and .410. The common lengths are: 

For 12 Gauge – 2 ¾ inches, 3 inches, and 3.5 inches

For 20 Gauge – 2 ¾, 2 ⅝, and 3 inches

For 410 – 2.5 inches and 3 inches

Super Short Shells 

I’ll mention these because they have become quite popular in the last couple of years. These 1 ¾ inch shells are for 12 gauges only and can be buckshot, birdshot, and slugs. They extend the capacity of a shotgun significantly and have very low recoil compared to full-sized shells.

Shotgun Caliber Types 

There are three main categories of shotgun calibers and these different categories typically determine what you are going to do with that caliber. There is also specialty ammo that we’ll briefly talk about, but for the average civilian these are not a major concern.  

To understand shotguns and shotgun ammo you have to understand shot. A “shot” is a term that describes several spherical balls packed into a shotgun shell. Shot varies in size as well as the number of projectiles in a shell. The larger the projectiles the less of them you can cram in a shell and vice versa.


Buckshot is a larger size of shotgun caliber primarily dedicated to killing medium-sized game. The buck in buckshot is a reference to killing deer. Buckshot varies in size, but the majority of sizes are capable of defensive use. Shot sizes are range between 0000 to T. Sounds confusing right? Well, let’s break it down and make it a bit simpler. 

You can find each and every size here.

0000 – Pronounced Quadruple Ought: A Semi-custom load made up of 9.5mm pellets designed for power and penetration. Perfect for hunting feral hogs and even bear. It is incredibly powerful and features sharp recoil. 

000 – Pronounced Triple Ought: A powerful load designed for medium to large game. It offers 9.1mm sized shot and is well suited for hunting. It does feature some heavy recoil. 

00 – Pronounced Double Ought: The most common buckshot load for 12 gauges. Used for defensive shooting and hunting. An excellent balance of both power and managed recoil. 

0 – Pronounced Single Ought: Single Ought offers a similar-sized shot to 00 with less recoil. Best suited for those who are recoil sensitive and want a good defensive and hunting load. 

#1 Buck – #1 buckshot offers an excellent balance of shot, power and recoil control. #1 buckshot is slightly uncommon but excellent for home defense and hunting medium-sized game. 

#2 and #3 Buckshot – Buckshot designed for 20 gauge shotguns that offer both effective shot size and shot amount for the smaller 20 gauge shotgun. 

#4 buck is a good hunting round for fixed choked shotguns and has declined in popularity as shotgun chokes have gotten better at controlling shot. It has had a slight resurgence for home defense use. 

F and T buckshot loads also exist and these odd types of buckshot are best suited for hunting moderate-sized animals like coyotes.


Birdshot is a shotgun caliber named because it’s designed to be effective against birds. It’s small enough to kill birds without damaging them extensively. It also casts a wide net that makes it easy to hit moving targets. There are tons of different birdshot loads available for different sized birds. Here is a quick rundown of most birdshot loads. 

You can find each and every load here. 

#9 Shot – The smallest of birdshot, best used for clay pigeons and not live birds. 

#8.5 Shot – Another small shot designed for clay pigeons, but offers slightly more recoil as well as more range than #9.

#8 Shot – Another popular load for clay pigeons, but it can be used for the smallest of game like rabbits, squirrels, and doves.

#7.5 Shot – Perfect for small birds like doves. It’s also cheap, common, and excellent for training purposes. 

#7 Shot – Small shot designed for dove, grouse, and pheasant. Also great for bigger squirrels. 

#6 Shot – This mid-size birdshot can be used for game as large as ducks at short ranges, but also perfect for squirrel and head shotting larger birds. 

#5 Shot – This shot size goes for bigger birds and is another excellent choice for duck hunting at most ranges. Will also take birds like pheasants at a distance. 

#4 Shot – This is different than #4 Buck. It’s a large birdshot size designed for taking birds as big as Turkeys. 

#3 Shot – Designed for large birds like turkeys and waterfowl. Provides more range and power than Number 4. 

#2 Shot – This load is excellent for hunting geese and delivers excellent penetration. It’s also a good choice for hitting moderate-sized birds at greater distances. 

#1 Shot – A shot load that’s kind of hard to find. It does deliver a lock of knockdown power for hitting large birds like geese at greater ranges. 

BB Shot – The largest birdshot that can be used for bigger birds, as well as smaller mammals at close range.


Slugs are solid projectiles like rifle rounds and are incredibly potent. They extend the effective range of a shotgun to 100 yards and cna drop deer, bears, and people. Slugs are powerful and come in a variety of different weights designed for different tasks. Slugs will vary based on your needs. You’ll choose a slug based on your task as well as its weight.

Looking for a Slug? Then you came to the right place. 

Specialty Calibers

Specialty ammo for shotguns are popular and range from useful for niche tasks to just fun stuff. Niche specialty ammo includes less-lethal loads of rubber buckshot or rubber slugs, as well as rounds designed to breach locks at close quarters. 

Fun rounds include things like dragon’s breath that blasts a flame 25 feet from the barrel of the gun. Other fun rounds include flares, fireworks, and other loads designed for less serious uses. Specialty rounds aren’t a major concern when it comes to serious use of shotguns unless you are military or police.

Parting Shots

Shotgun ammunition seems confusing, but in reality, once you establish what your goal is you can choose the right load for you. Shotguns are powerful, versatile weapons and mastering round selection is an important task. Once you do, you’ll begin your mastery of the shotgun. 


Travis Pike is a former Marine Machine gunner who served with 2nd BN 2nd Marines for 5 years. He deployed in 2009 to Afghanistan and again in 2011 with the 22nd MEU(SOC) during a record setting 11 months at sea. He’s trained with the Romanian Army, the Spanish Marines, the Emirate Marines and the Afghan National Army. He serves as an NRA certified pistol instructor and works as a firearms writer.

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