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.