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Defensive Tactical Training's Blog - Reporting News relative to the defensive use of firearms and handguns.

What is all the talk about Caliber?

.22 LR, 9mm, .380, .45, oh my! What do all these random numbers on bullets mean and which one should you buy?

Whether you’ve already bought your gun or not, it’s a good idea to get an understanding of the different types of ammunition and which will best serve your purposes.

There are many types out there, but only a few are very common — and for good reason. They do an excellent job.

Let’s look at the common ones here.

What Is Caliber?

First of all, the caliber simply refers to the diameter of the gun barrel and thus which size cartridge will fit into it. When we are speaking of ammunition, Caliber is a measurement of a bullet’s diameter. It can be measured in both inches and millimeters (mm). For example, .45 ACP has a diameter of 0.451 inches and 9mm has a diameter of 9.01 mm.

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