Caliber is the approximate diameter of the inside of the barrel on a firearm or the diameter of a bullet, and is usually expressed in inches or millimeters. In addition to using different units of measurement, different countries sometimes use different methods of measuring caliber. Because of these factors, deciphering the actual diameter of a bullet or the bore size of a firearm can be bewildering.
However, I'm attempting to clear up some of the confusion in this article. Switching between the metric millimeters and imperial inches systems of measurement is relatively straightforward. There are 10 millimeters mm in 1 centimeter cm and 2. Therefore, when a caliber is given in inches, multiply it by The opposite is also true: divide a caliber expressed in millimeters by If you are looking for an approximation of the bore size or bullet diameter, that is all you need to know.
To convert caliber to millimeters, multiply the measurement in inches by Conversely, to convert millimeters to inches, divide the diameter in millimeters by For the mathematically challenged, you can just plug numbers into this handy online conversion calculator. Typically, you can see the caliber of the firearm stamped right there it. In older firearms, it can be difficult to read the imprinted text. In addition to using different units of measurement millimeters versus inches , there are also different measuring methods.
The caliber of a rifled barrel is generally measured in one of two ways. As always, there are some exceptions to these rules. Like most cartridges born in the U.
The bore of a. However, the actual diameter of the projectile in a. This is because the bullet must be larger than the distance between lands to form a proper seal in the barrel. To generate sufficient spin, the projectile must match the groove diameter rather than the land diameter.
The only surefire way to avoid the complications of improperly sized projectiles is to use ammunition designed for your specific firearm. If you like to load your own ammo, be sure to use a respectable reloading manual. This way you can reload with confidence, knowing for certain you are using properly sized bullets to hand load a particular cartridge. If you flip through any reloading manual you will see a seemingly endless listing of bullet diameters.
Some of these differ in mere fragments of inches. Gun people seem to like variety. Certain shooting applications require different types of projectiles. All you would see is a puff of fur. It is the spice of life, after all. Attempting to shoot a bullet just a few thousandths of an inch too large for the barrel can be extremely dangerous. While it may seem obvious, the way to avoid problems with improperly sized bullets is to shoot the right ammunition in your guns.
When you see that nomenclature, the first number describes the diameter of the bullet and the second number describes the length of the cartridge case used also known as case length. So, the 7. How do you determine its caliber? They do range. The second number denotes the length of the barrel from breech to muzzle measured in calibers. Hope this helps, John. Could you do more examples? Can that be? However, there is a big difference between those two cartridges otherwise.
Check out this article to see a photo of a. Hope this helps! What caliber rifle did it come from? Where do you live? Can you email a photo of the bullet to john at thebiggamehuntingblog. We might be able to determine what rifle it came from. Finally, how about the 6. Turns out to be almost the same as a inch caliber. So, multiply a metric mm caliber by either 3. Something else that adds to confusion is when a caliber is stated like a , , 6.
The is a caliber in a necked-up case. For the 6. So, the 7. The point of the article is simply to help make the conversion and understand the cartridge. A good discussion can be found at the links below, and it also includes a chart showing U. Standard aka Imperial versus the metric mm equivalent, and many of the cartridges that fall in that family.
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