Throwback Thursday: Understanding Shotgun Shells 101

Shotgun with shotshells ranging from 12 gauge to .410

The shotgun is designed to throw a group or “pattern” of many small pellets called “shot,” which makes hitting a flying or moving target much more feasible than using a single projectile, as fired by a rifle or pistol. Because it utilizes numerous pellets instead of a single bullet, a shotshell is constructed differently than a cartridge for rifles or pistols. So, instead of the rifle or pistol cartridge’s brass case that contains primer, powder, and bullet, the shotgun’s shotshell consists of a hull that contains the primer, powder, shot wad, and an amount of shot.

There are many different shotgun bore sizes or “gauges” (much like rifle and pistol caliber size), and gauges of differing shell length and all can be loaded with a wide variety of shot sizes. Let’s break down some of these terms so you can better understand your shotgun or make a well-informed purchase the next time you head to your favorite gun store or range.

Remington 1100 shotgun with 3 shotgun shells
The shotgun is designed to throw a group or “pattern” of many small pellets called “shot,” which makes hitting a flying or moving target much more feasible than using a single projectile, as fired by a rifle or pistol.

Gauges of Shotgun Shells

The term “gauge” is an old one. It refers to the measure of the bore diameter of the shotgun. With the exception of the .410 Bore, which is not a gauge at all (it’s actually a caliber) but often mistakenly called one, the gauge number is equal to the number of lead balls of that bore diameter that add up to weigh one pound.

For example, 12-gauge, the most common shotgun gauge today, is the diameter of a ball of lead weighing 1/12-pound of lead, while a 20-gauge is the diameter of a lead ball weighing 1/20-pound of lead. It’s not hard to see that it takes more lead balls in 20-gauge to equal a pound than it does a 12-gauge, thus, the 20-gauge bore diameter is smaller than a 12-gauge.

The common lineup of gauges made today (from smallest to largest) are .410 Bore (again, not actually a gauge, but a common shotgun chambering), 28-gauge, 20-gauge, 16-gauge, 12-gauge, and 10-gauge. (Shotguns of long ago also included the mammoth 8-gauge and 4-gauge, and the smaller 24-gauge and 32-gauge, but these are all collectors’ items now.)

The smaller gauges are generally used for clay target shooting and hunting smaller birds and game animals, while the larger gauges are commonly employed for clay target games, personal defense, and for hunting the larger game species like turkey and deer.


The bunch of little pellets a shotgun fires are collectively called “shot.” They are often pure lead, sometimes lead coated with another material like copper, or of non-lead components such as steel, bismuth, tungsten, and other materials.

The shot sizes are numbered beginning with the smaller “birdshot.” Eventually, the sizes are stated in letters. Finally, there are the largest “buckshot” sizes, popular for use on deer in the southern U.S., for hunting fur bearing varmints, and self-defense.

Shotgun with shotshells ranging from 12 gauge to .410
From left to right, modern shotgun shells from 12-gauge to .410-bore.

The finest (smallest-diameter) shot sizes (in order starting from the smallest commonly available size) are Nos. 9, 8, and 7 ½. These are the sizes you’ll traditionally see on target loads for clay shooting, but they also have applications for some upland game birds such as ruffed grouse and woodcock.

The next group of shot sizes (still in order) includes Nos. 6, 5, and 4. These work very well for pheasants, ducks, sage hens, rabbits, and squirrels; heavy “charges of shot” (the amount of shot or shot “payload,” usually given in ounces) in these shot sizes will give good results on turkeys as well.

The big shot sizes, Nos. 3, 2, 1, B, BB, BBB, T, F, and FF shot are used for long-range waterfowl hunting, as these large pellets will hold their velocity and retain enough energy for quick kills on distant geese and ducks.

Buckshot nomenclature runs from No. 4 Buck (diameter .220-inch) to 000 (pronounced “triple-ought” or “triple-aught”) Buck (.360”), so as it is with other shot sizes, the higher the number the smaller the pellet size, and the more zeros in the “aught” size, the larger the pellet diameter. Buckshot is very effective on game such as deer, fox, and coyote within 60 or so yards and it can make a sensible home-defense choice depending on your surroundings and situation.


So far I’ve talked about a shot being a group of pellets, and it is. But shotgun shells also fire single projectiles called “slugs.” Generally reserved for big-game hunting such as deer and sometimes bear, slug shotguns can have a traditional smoothbore like all shotguns that fire shot pellets, but most slug shotguns used for hunting big game or for use in some competitive shooting such as 3-Gun have “rifled” barrels, just like the barrel on, well, a rifle! Such barrels have twisting lands and grooves cut into them that help spin and stabilize the shotgun slug to enhance accuracy. Slug shotguns are specialized shotguns and a class unto themselves.

Kay Miculek pointing to a white silhouette target
World Champion Target Shooter and Babes with Bullets instructor, Kay Miculek, demonstrates the difference in shot pattern between Bird Shot (Left) and Buck Shot (Right).

Shotshell Length

Shotshells come in different lengths within their respective gauges. This is very important to understand because stuffing a shotshell into your gun that’s too long for its chamber — and even though it may be the correct gauge — can be extremely dangerous. A good, safe rule of thumb is to only use shotgun shells as long or shorter than the markings on your shotgun barrel say you can use. Let’s look at an example.

Today’s 12-gauge shells come in 2½-, 2¾-, 3- and 3½-inch lengths (and they all hold different amounts of powder and shot charges). If your shotgun is marked “12-gauge 2¾-inch” you may safely fire 2½- and 2¾-inch 12-gauge shotshells, but not the 3- or 3½-inch. If, on the other hand, your shotgun is marked for 3½-inch shotgun shells, you can safely fire any of the 12-gauge shotgun shells.

(Note: Not all shotguns that can safely chamber all lengths of a particular gauge will always fire all of them reliably. This is especially true of many semi-automatics. Always consult the owner’s manual for your gun to determine what loads are best recommended for it.)

It’s vital to understand that at no time can you interchange different gauge shotgun shells. Such a mistake can destroy a gun and result in serious injury to both the shooter and bystanders. Never chamber a shotshell in a gun without checking both the shotshell and the gun for compatibility, and always consult the owner’s manual for any newly acquired gun to ensure you’re using the correct ammunition for it.

Three shotshells ranging from a 3-inch magnum to 2 3/4-inch in length
These are all 12-gauge shotshells, but they are all of different lengths. Always double-check your gun and its owner’s manual to determine exactly which shell lengths your gun is made to handle safely.

The High Brass vs. Low Brass Myth

If you’re a new shotgun hunter, one of the things you’ll notice in retail stores are boxes of shotshell ammunition marked “high brass.” This high brass, the portion of the shotshell that houses the primer and holds the plastic hull, is the source of some old wive’s tales that just won’t go away. Let me explain.

When I was a younger man, I was taught that the difference in the height of the brass rim was indicative of the power or velocity of the shotgun load. The longer the brass, the hotter the shell and the faster the shot traveled after it left the muzzle. High brass was more powerful than low brass. That may have once been true, but not anymore. When purchasing shotgun ammunition, ignore the length of the brass rim and pay attention to the labeled velocity and payload of shot (again, stated in ounces) of the shell.

Do you have a tip about shotgun shells or an interesting bit of trivia? Share it in the comment section.

Editor’s note: This post was originally published in May of 2019 It has been completely revamped and updated for accuracy and clarity.

The Mission of Cheaper Than Dirt!'s blog, The Shooter's Log, is to provide information—not opinions—to our customers and the shooting community. We want you, our readers, to be able to make informed decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (22)

  1. I have a 1908 L.C. Smith 12ga. SxS. What shell length 2.5 or 2.75 for this gun. Or can I just measure to the forcing cone in barrel? It measures 3″ to beginning of cone so assuming it’s 2.5 shells. There is a little pitting right before the cone on one side, not deep or bad. Damacus twist barrels. RSTShells offers shells that can be used? What is the consensus on being able to shoot this shotgun on dove field next year or taking on Quail hunt in October?

  2. Now we just need a discussion on shot size vs choke size. I’ve got a extended coyote choke and turkey choke that I can’t remember the size’s of at the moment. But I do know you have to be very mindful of what size and type of shot. Some will not take steel shot and larger lead. It’s a fine line between tight patterns and shot size.

  3. OLDPROF49: I found this bit of information which may answer your question.

    Titled – Do not shoot a .45LC in a gun chambered for .410 shotgun.

    A .410 slug measures about .387 give or take a few thousands. A .45LC has a slug diameter of .452. It will cause a big BOOM in a .410 shotgun.

    A few select guns, most notably the T/C Contender pistol chambered in .45LC will shoot the .410 shells very well. It has a choke to install for their use though. It must be removed to shoot the .45LC.

    The overall dimensions of the 2 shells are so close that they are interchangable, but that can be deadly.

    A .45LC has the advantage in performance. Average bullet weight for it is about 225-250 grains. The .410 slug weighs in at about 110 grains. You may have a bit more velocity out of the .410, but more energy out of the .45LC.

  4. 12 gauge
    Low brass vs high brass,
    Come dove hunting with me, you bring low brass 7 1/2 and after a few shots, let me drop a high brass 7 1/2 in your chamber then try saying there’s no difference between the two, after you say OUCH!

  5. Hi Rich
    I just took a shotgun class and used a Mossberg 590 shockwave.
    It is smooth not rifled. The instructor told me the slugs that are rifled are made for smooth bore barrels. Since there is no rifling in the barrel the slugs rifling makes up for it and is more accurate. WELCOME BACK to shooting !!! Try a 20 guage shockwave and you will have the time of your life !!!!! Enjoy ! J.B

  6. Do you need to have a rifled barrel for rifled slugs? What is a sabot round? Do you need a rifled barrel for sabot rounds!

  7. thanks for this article it great to have it explained like this I have a better understanding of how many different types of gauges an types of shot

  8. I have an Ithica 12 ga. shotgun, original barrel is 2-3/4″. I recently bought a replacement slug barrel that’s marked 3″ what determines length limit. Is it the barrel, or the receiver ? if it’s the barrel, would the receiver cycle 3″ shot shells ?

  9. Are there slugs made for my old smooth bore 16 ga Ithica Shotgun? I am looking to get back into shooting after a 60 year hiatus. I noted that some slugs now days are rifled. Can they be used in a smooth bore or should I search for smooth bore slugs?

  10. 8 gauge shells—at least as recently as 2002—were used to blast the walls of cement kilns. Winchester produced an “industrial 8 gauge” with OO, #2, and #4 shot. I knew a man who did the shooting at the cement plant in Rapid City, SD.

  11. My Mossberg 590 will not handle low brass shells, The low brass shell expands when fired and will not eject. Have to dig it out manually. Got to have high brass.

  12. I have a Remington 870 12 ga that’s marked 2-3/4 shell length on the gun. I also have a slug barrel that’s marked 3 in. So can a 3 in shell be used with that slug barrel with the gun marked 2-3/4?

  13. Excellent article, packed with simple and safe information for easy understanding.

    Thank you and Semper Fi

  14. One additional cautionary note may be to avoid shooting with friends with mixed gauge sizes. It is so easy to mistake a 20 ga. shell with a 12 ga. or visa versa.

    1. Excellent point Bob. The 20 ga. will drop into a 12 ga. chamber and then you have a deadly catastrophy. 20 ga. shells used to come in various colors. All modern 20 ga. shells are now yellow.

  15. Something worth mentioning: shell length is actually measured after the shell is fired and the hull has fully expanded outward.

  16. I have also heard, and learned, that “high Brass” was better for reloading than “low brass” and to always be sure that the base metal was brass and not steel as the steel material is very hard on the ejector of the shotgun. True? False?

  17. Excellent article! I learned quite a bit about shotgun nomenclature. 4 gauge? Really? If I’m correct, each “pellet” would weigh 1/4 lb.! I do have a question about .410. If that is the caliber, how can it be used successfully in revolvers that also chamber .45 Colt? I assume their bore diameter is .450. Isn’t that too big for a .410 shell? Apparently it’s not inherently dangerous, but accuracy must really suffer.

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