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Hunting 101: Bullet caliber

January 1, 2010

Caliber measures the diameter of a bullet -- the projectile that flies from the barrel of a gun when it is fired. How fast it flies and how hard it hits depends on how much gunpowder propels it from the case -- the (usually brass) container that holds the powder and seats the bullet. The entire unit -- bullet, case, powder charge and a primer to ignite the powder -- is called a cartridge.

Bullets must be measured with extreme precision - down to a thousandth of an inch - and a bullet's size can be stated in inches or millimeters. For example, a .25-caliber bullet has a diameter of a quarter-inch; a .338-caliber bullet measures about a third of an inch. Others are stated in metric terms, like the 7-millimeter. Factory bullets range in size from the teensy .17-caliber favored by prairie dog shooters up to the whopping .458 Winchester Magnum and the .460 Weatherby Magnum, both of which can take down an elephant. Custom rigs can go even bigger, but most hunting in North America takes place in the .25- to .35-caliber range.

Think of caliber as a continuum. Starting with those little .17s and edging up to the .22 magnums, you're looking at small, fast, flat-shooting cartridges that are good for little critters at longer distances, like prairie dogs and coyotes. When you move up to the .243 and .25-06 range, you're still talking about a flat-shooting cartridge, but one with a little more oomph. This is pronghorn country and edging into whitetail deer. Once you get to the .270, 7mm and .280 level, you're firmly into whitetail and mule deer range and edging toward elk. The .30-caliber family - the .308, .30-06 and .300 Winchester Magnum - are extremely versatile and can be found in plenty of deer and elk camps, as well as in the hands of moose and black bear hunters. The 8mm, .338 and .35 calibers are more about moose and bigger bears.

The "magnum" designation generally means the manufacturer created a larger casing that holds more powder, which in turn propels a bullet with more speed and power. For example, the bullet size is exactly the same for a .308, a .30-06 and a .300 Win Mag. But those case sizes are all different. Notice the squared shoulders of the .300 Win Mag compared to the .30-06. That little bit of extra powder gives that round a little more pop.

Shooting purists and hand-loaders (often the very same guy) are all about velocity; faster bullets drop less over distance, making them more accurate at longer range. That's why they're constantly pushing speeds to 3,000 and 4,000 feet per second. For a hunter, the more important number is terminal energy: the number of foot-pounds the bullet delivers to the target. Experts say 1,000 foot-pounds is a safe number to take down a deer, and you need closer to 2,000 for bigger game such as elk, moose and bears. Just remember: You can study the ballistics until your eyes melt, but that's no substitute for knowing your weapon and the ammunition you plan to shoot animals with. A clean, accurate shot trumps all the little numbers on the box -- as long as you're using an appropriate caliber for your quarry.




July 15, 2011 9:31 PM


September 14, 2011 2:31 AM


excellent concise and easy brief - good job!
December 7, 2012 10:44 AM
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