How to Explain the Difference in Rifle Ammo Calibers

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There are plenty of excellent reasons for wanting to be able to distinguish between different forms of ammunition. For hunters, it is instrumental that they choose the right round for the game they are pursuing. For others, it may be a safety concern or simply a point of interest. For deciphering the caliber of rifle bullets, basic attention to numerical markings on the round and its packaging is the first step.

Look at numbers. The caliber of any weapon or ammo is usually represented in numbers, such as 17, 22, 37 or 45. After you locate this number, you can go into more detail. (see ref. 2)

Isolate units. The caliber of a bullet or piece of ammunition refers to the object's diameter, so the number you find accompanying the ammo is a measurement of this. This will be found, typically, either in inches or in millimeters such as Colt 45 (in) or 9mm. Ammunition usually comes with both designations listed even if one is a more popular way of referring to the round. (see ref. 1 & 2)

Move the decimal point. If the ammunition is listed in millimeters, you don't have to do this due to the fact that the actual measurement is present. If the ammo is in inches, then a number like 45 or 357 is not the real measurement. The decimal must be moved over so that the lead number is in the hundredths position as so-- .357 or .45. This is the true diameter in inches. (see ref. 1 & 2)

Consider numerous factors. Just because a rifle round has a larger diameter does not indicate that it is necessarily more powerful than a smaller round. Power depends on caliber, weight in powder grains and other criteria such as muzzle velocity. All of these factors should go into your choice of hunting or defense round. (see ref. 2)

Compare types of arms. The caliber can tell you something about the type of weapon or firearm it is used in. Any round that is 20mm or less is commonly referred to as small arm ammo. This is better for small game such as rabbit or fox. Medium size calibers usually center around 25 caliber rifles and are good for deer, boar and similarly sized quarries. Large caliber rounds and weapons should be reserved for such big game animals as bear, elk or moose. The average size large caliber round is 270. (see ref. 3 & 4)


  • Always make sure that the proper round is loaded into the firearm to prevent accident, injury and damage to the weapon.
  • Higher caliber bullets than are necessary in a hunting scenario can destroy a prize animal.


About the Author

Geoffrey St. Marie began writing professionally in 2010, with his work focusing on topics in history, culture, politics and society. He received his Bachelor of Arts in European history from Central Connecticut State University and his Master of Arts in modern European history from Brown University.

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