The shotgun world is a mess of old standards & notations, and nowhere is this more evident
than the way we define bore diameters. Just about everyone is familiar with the terms -
12-gauge, 20-gauge, etcetera - but what exactly does gauge mean, and how does it translate
to an actual diameter? Well, to answer that properly, we have to
go way back. In the Napoleonic era, cannons were commonly
described by the weight of the shot used in them. An iron cannon ball sized for a 12-pound
gun, for example, would weigh 12 pounds - at least in theory.
Some of the smoothbore, muzzle-loading small arms of the time adopted a similar notation,
where their bore diameters were described by the number of matching lead balls that
could be cast from a pound of lead. A musket for which 12 round-balls could be made out
of a pound of pure lead would be known as a “one-twelfth-of-a-pounder”; or 12-gauge
or 12-bore for short. The math here isn’t too complex.
The mass of a ball is simply volume times density, and since the gauge is the number
of balls per pound, it is equal to the reciprocal of the ball’s mass in pounds. This lets
you easily work out the gauge equivalent of any bore diameter if you know the density
of lead. To find diameter from gauge, simply rearrange
the equation. In addition to single projectiles, these old
smoothbore firearms could be loaded with multiple smaller shot if an application called for
it, even if they weren’t specifically designed as “fowling pieces”. While modern rifle
barrels have seen significant technological advancements and design changes since the
smoothbore days, shotgun barrels have remained virtually unchanged apart from some material
and structural improvements, and are still usually defined by gauge today.
With old muzzleloading shotguns, the gauge could be pretty much anything the gunsmith
or customer fancied. All that really needed to be sized to the bore were the wads, and
most users simply cut those themselves. But with the advent of self-contained, mass-produced
shotshells, along with more complex breech-loading and repeating shotguns, ammo manufacturers
and gunmakers began to focus on smaller numbers of standardized gauges. This trend continued
as advancements in powders and components improved and expanded shotshell capabilities
across the board, and as a result, only a handful of the most popular gauges remain
in use today. The largest you’ll see on gun store shelves
now is the 10-gauge, which has a theoretical bore diameter of .775 inches.
Long since superseded by the 12ga as an all-around chambering, the 10ga lives on today primarily
as a waterfowling gauge, since its big 3.5” shells can hold large quantities of low-density,
nontoxic shot. Though with its newer 3.5” super magnum spec and improved nontoxic shot
materials, the 12ga is no longer far behind. You can also find buckshot, slugs, and heavy
lead birdshot loads for the 10ga, but again, these won’t really let you do much you couldn’t
with a less bulky 12ga shotgun. The 10ga is fine if you’re into the novelty
of the big shells, or you want a dedicated waterfowling gun for use with steel shot.
Otherwise, the 12ga can be about as effective, and is much more versatile and widely-available.
Our formula spits out a standard diameter of .729 inches for the 12ga. Actual bore diameters
can deviate from this, but they usually land between .725 and .735 inches.
Since the early 1900s, the 12 has established itself as the leading all-purpose gauge, and
is easily the most popular size in use today. It’s large enough to pattern well with just
about any common shot size, and its typical lead shot payloads of between 1 oz and 1 ¼
oz are very well-balanced for sporting, hunting, and combat alike.
Because of the 12ga’s popularity, light loads of 7/8 oz or less are also available,
as are magnum loads of up to 1 7/8 ounces. The higher-pressure 3.5” 12ga super magnum
introduced in the late 1980s can send 2 or more ounces of lead downrange.
Reloaders enjoy an enormous amount of support for the 12ga, and no other chambering offers
the same variety of factory buckshot, slug, and novelty loads; or such inexpensive and
easy-to-find practice ammo. If you want one gun that you can use for everything
and always find ammo for, the 12ga is the clear winner.
The 20ga shotshell, with its characteristic yellow hull, is also a very popular size.
Both math and standard specs assign the 20ga a bore diameter of .615”.
The standard 20ga birdshot load is 7/8 of an ounce of lead shot, though magnums can
contain up to 1 ¼ or 1 5/16 ounces. There are also a variety of 20ga slugs available
for use in both smoothbore and rifled barrels, along with buckshot loads suitable for personal
defense and some hunting. The 20ga’s narrower bore leads to shells
and guns that are noticeably more compact and easier to carry than 12ga equivalents,
and its typically lighter payloads produce less recoil. This makes it very well-suited
for most upland hunting, as well as an excellent choice for younger or smaller-statured shooters.
It’s also an effective and family-friendly home defense gauge.
With the 20ga’s reduced shell volume, it doesn’t perform as well as the 12 with large
shot sizes or heavy payloads, and larger buckshot pellets don’t stack well in the narrower
space. So it can’t match the capabilities of the bigger and more versatile 12ga for
certain things like waterfowl hunting or long-range trap. Those applications aside though, the
20 is a very useful, capable, and popular gauge, a favorite of many shotgunners.
Between the popular 12 & 20 gauges lies the much less prevalent 16-gauge, with a theoretical
.663-inch bore diameter, though you may also see it described as .662 or .665.
As its gauge number suggests, the 16ga is practically tailor-made for a one-ounce shot
load, but it also does well loaded down to 7/8 of an ounce, or up to 1 ¼ ounces. It
can handle shot big enough to knock just about anything out of the air, and it’ll even
fit larger buckshot reasonably well. The 16ga has a special place in the heart
of many shotgunners, who view it as a “gentleman’s gauge” of years past; the kind of shotgun
the Most Interesting Man in the World would probably use. More practically, a 16-gauge
bore strikes a very nice balance between the versatility of the 12ga and the compact size
of the 20, and it was a very widely-used small-bore gauge up until the 20ga overtook it in the 1970s.
There are a number of reasons for its current
status, including the absence of a 16ga skeet class, competition from the 3” 20ga introduced
in the 1950s, and its limited capacity for low-density nontoxic shot.
But a more fundamental issue is that with modern components and loads, there really
isn’t much of a niche for the 16ga in its current form. Looking purely at shot size
and payload weights, a 2.75” 16ga load won’t do anything that a 12ga or magnum 20ga couldn’t.
And on top of that, ammo companies and gunmakers seem to have pretty much given up on the 16ga.
It still hasn’t received the 3” magnum spec it needs to be a competitive multi-purpose
chambering, and many current- and recent-production 16ga shotguns from major manufacturers are
simply under-bored 12ga designs with no weight or size advantages.
The 16ga isn’t dead yet though, and while it’s not as popular as it once was, it is
still a very well-balanced gauge, and there are a lot of older 16ga shotguns still in
circulation. If you’re in possession of one of these “sweet sixteens”, you can
still find a wide enough variety of birdshot, buckshot, and slugs to hunt most game, and
any gaps can easily be filled by reloading. What the 20ga is to the 12, the 28-gauge is
to the 20. The 28ga has a bore diameter of .55 inches.
Typical loads contain ¾ of an ounce of birdshot, but you can also find some heavier loads of
7/8 or one ounce. Shot sizes up to #4 are available, though the wider 20ga would tend
to handle #6 and larger shot better. Slugs exist for the 28-gauge, but they’re not
too common; and if you want buckshot you’ll probably need to handload it.
Really though, if you want slugs, buckshot, and heavy 1-ounce payloads, you might as well
just go with the 20ga. The little 28 is at its best as a soft-shooting upland and skeet
gauge. Purpose-built 28-gauge shotguns can be even lighter and trimmer than 20-gauges,
but they’ll still dust clays and kill birds cleanly with a little skill.
It probably wouldn’t be a great choice for new shotgun owners since 20ga shells are easier
to find, less expensive, and more versatile. But the little 28 has a healthy following
among experienced shotgunners, and it isn’t difficult to see why.
The smallest common shotshell size is the .410, which is a bit of an oddity. As you
might have guessed from the preceding decimal point, this isn’t a gauge, it’s a caliber.
.410 shotguns have bore diameters of .41 inches, which is roughly 67 ½-gauge.
The standard load for the 2 ½” .410 is just half an ounce of birdshot, while 3”
shells can contain 11/16 or ¾ of an ounce of shot. Birdshot sizes up to #4 are available,
though anything larger than typical target shot doesn’t tend to pattern well. .410
slugs are very lightweight, typically 1/5 or ¼ of an ounce.
The .410 is not a terribly versatile chambering, but it does have some uses. With just a paltry
half-ounce of shot on tap, breaking clays becomes quite the challenge, and there’s
a special .410-only skeet class. It is also useful for close-range pest control, and the
very small size and light weight of .410 shells and guns has led to their frequent inclusion
in emergency survival kits. Some consider .410s to be good youth guns,
and many a lifetime shotgunner got their start with a simple .410 single-shot. However, others
argue that the .410’s minuscule payloads and thin shot patterns are more likely to
just frustrate beginners, and a similar shotgun in a larger gauge would be a better and more
useful choice for most young shooters. More controversial than that though, is the
idea of the .410 as a defensive cartridge. Recent years have seen the introduction of
a number of .410 firearms marketed as self-defense pieces, as well as a plethora of new .410
buckshot and slug loads intended for use in those guns.
Those who fancy the .410 as a defensive chambering often do so under the idea that since it’s
a shotshell, it must pack the punch of a shotgun. I explained in the previous video in this
series how buckshot’s legendary stopping power is all about quantity over quality.
Well, the .410 can’t really offer that quantity; a load of .410 buckshot is about equivalent
to a few FMJs from a small-caliber pocket pistol. While that that could be an effective
stopper (at least at close range, before the deformed pellets have a change to spread),
it doesn’t really compare to the power of even non-magnum buckshot loads from a full-sized
shotgun. But while an argument could be made for .410
buckshot, .410 slugs don’t offer much in comparison to other pistol rounds. Despite
their size, they only weigh about as much as .380 ACP bullets, and are far less advanced
than the jacketed hollowpoints used in modern defensive handgun ammunition. If you’re
thinking of getting a .410 for use primarily with slugs, you’d probably be better-served
by a similar firearm in a more conventional cartridge.
Well, that about wraps up the modern shotshell options. Virtually all current-production
shotguns are chambered in one of these six gauges.
However, there are a few other gauges that still see some use today.
Two of these are the 24-gauge and the 32-gauge, which perform similarly to the 28-gauge. There
are a number of old 24- and 32-gauge shotguns still taking game or breaking clays, and components
and even loaded shells are available to feed them.
On the other end of the size scale is the old 8-gauge. Though long since rendered obsolete
for hunting, it currently has some industrial applications, and there are still working
8ga guns in the hands of collectors, so sources exist for 8ga ammo and components.
Finally, there are the really rare shotshell sizes that are no longer used, but are still
studied and collected by hobbyists. These include the experimental 14ga Winchester
toyed with introducing in the 1960s, “garden gun” shells even smaller than the .410,
4-gauge and larger punt gun shells, and a whole bevy of other oddball gauge, inch, and
metric sizes. But unless you’re a big collector, these
six sizes are what you’ll be dealing with as a shotgun owner today.
Hopefully this video was a good introduction and overview for these. If you’re here trying
to decide what gauge to get into and you still have questions, I’ll be happy to answer
them as best I can. Generally though, for new shooters, I’d
recommend the 12 gauge as a solid do-everything shotgun; the 20 if you want something a bit
lighter and softer-shooting for home defense, skeet, or upland hunting; and the .410 for
plinking, an ultralight survival gun, or maybe a starter shotgun for younger kids who can’t
quite handle a 20. Until next time, please have fun and shoot
safely and responsibly.