Caliber is essentially the size of the projectile.
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The diameter of a bullet is known as the caliber. Generally, the larger the caliber the larger game it can take down. Caliber is either measured in millimeters, or thousandths of an inch.
For example, a 9mm pistol would have a bore diameter of 9mm, and a .45 would have a bore diameter of .45 inches. |
Common Caliber Sizes
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The caliber is distinct from the cartridge, which not only describes the bore diameter, but also the chamber dimensions. For example, .45 ACP has the same bore diameter as .45 Long Colt, but the chamber dimensions are different. |
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When the bullet is fired, an enormous amount of pressure builds up on the neck of the round. Since the bullet is the same diameter as the bore, it plugs the bore by pressing tightly against the internal surface of the barrel. As the bullet travels along the inside the barrel, it follows helical grooves on the bore’s surface, which rapidly spins the bullet as it travels down the barrel.
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