What caliber are you shooting? That's one of the first questions other
shooters ask when they meet you at the range or in the hunting fields. But it's
not what they mean.
The "caliber" question is really a "cartridge" question. Caliber is the
diameter of the rifle's bore. Answering it correctly does not describe the
ammunition the rifle fires. You can shoot a 30-caliber, but the cartridge could
be a .30-30 Win., .30-06 Springfield, .300 Win. Mag.,
.300 Savage, .300 Wby. Mag., .308 Win., .30 AR Rem., .300 Blackout, .300 Win. Short Mag., .300
Rem. Ultra Mag, .300 Dakota, .300 H&H Mag, .300 Norma Mag,
.30-378 Wby. Mag... .
For clarity, it's important to know the differences between bore caliber,
bullet caliber and cartridge.
Bore caliber is the diameter of the bore, the hole in the barrel. If that
hole is rifled (spiral grooves cut into it,) some would reference the diameter
across the bottom of the rifling grooves. This is why some shooters refer to
.30 calibers as .308 calibers. The .308-inch dimension is both the
groove-to-groove diameter and the bullet diameter. Bullets have to be slightly
wider than bores in order for the rifling to grip them. The bullets are the
same diameter as the diameter of the rifling grooves, and that's why you see
rifling marks or grooves cut into bullets after they've been fired.
When referring to sporting arms, caliber can be expressed in inches or
millimeters. The British and U.S.
tradition is inches. Other countries use the metric system. Thus, a .28 caliber
in the U.S. would be a 7mm
in Europe. A .264 caliber here is a 6.5mm, a
.308 caliber is 7.62mm, a .243 is a 6mm and a .224 is 5.56mm.
Cartridge is the proper name for the whole round, which includes primer,
brass case, powder, and bullet. The .30-06 cartridge shoots a .308 bullet
through a .30-caliber bore.
Some shooters refer to the cartridge as a bullet,
which can get real confusing. One gentleman was describing an accident in which
his cartridge apparently suffered head separation. That's when a brass case
breaks apart just above the head of the case. Generally the front half sticks
in the chamber while the extractor pulls the head out. But this guy described
his bullet as breaking in half inside the rifle, which is a whole 'nother matter. His description wasn't reaching his audience
because he didn't use the proper nouns to identify the parts.
Real confusion results from all the goofy names given cartridges. They often
make no sense. The .30-30 Winchester
is a .30 caliber, but the second "30" refers to the original weight of powder
in the charge. The 30 in .30-06 also refers to bore diameter, but the -06 is
the year it was created. The various .300 magnums are .30 calibers with an extra
zero added, perhaps to signify the extra velocity from the magnum dose of
powder. The .308 Winchester
muddies the water by using bullet caliber instead of bore caliber. The famous .22-250
Rem. is a .250-3000 Savage case necked down to .22 caliber. And so it goes.
Here is a list of popular bore calibers and bullet calibers that fit them:
Bore caliber in inches &
millimeters Bullet caliber in inches
Shop The Sportsman's Guide's great selection of Rifle Ammunition!
Ron Spomer has been photographing and writing
about the outdoors for nearly four decades. He's written seven books, hunted on
six continents and been published in more than 120 magazines. He's currently rifles'
editor at "Sporting Classics," Travel columnist at "Sports Afield," Field
Editor at "American Hunter" and "Guns & Ammo" -- Optics Columnist at "North American
Hunter," Contributing Editor at "Successful Hunter," Senior Writer at "Gun
Hunter," and TV host of "Winchester World of Whitetail." He will write on Shooting Tips weekly for sportsmansguide.com. You can read his
blogs and catch some of his YouTube videos at www.Ronspomeroutdoors.com.