In part 2 of the series, “Ballistics, Cardridge, & Ammunition Components,” I will be discussing bullet sizes in calibers and millimeters. I will discuss or demystify alot of the technical jargon that alludes many people. Hopefully by the time you are done reading, you will have a good understanding of the actuall size of the bullet.
To start off, there are two basic measuring systems in place for bullet sizes. Caliber and millimeter. Caliber is basically the U.S. measurement standard and millimeter is the European standard.
Caliber is very simply explained. It is a percentage of an inch. So if you have a “22 caliber” bullet, it is .22 inches. If you have a 30-06, it is .30 inches in diameter. If you took the measurement of the bullet at its widest point across the center of the bullet where it would cut it in perfect halves, you would measure the caliber.
When dealing with European arms, you will actually see a Millimeter (mm) designation. Just like the caliber, the mm is a unit of measuring very small distance. So the 7.62 is 7.62 mm in diameter. The military adopted this form of size when the U.S. joined NATO in order to reduce confusion in the field when standing side-by-side with our allys in combat. It allows the sharing of ammunition. So you may hear someone say something like, “7.62 Nato.”
Actually, the 7.62 mm is the same bullet size as the .30 caliber.
It is important to know that there are caliber based or mm based bullets that are interchangeable, but this doesn’t necessarily mean that they can be shot in the same rifle. The cartridge may be different sizes or the charge may be alot more powerful in one that the other. I wouldn’t want to be able to destroy my gun, or hurt myself by shooting a 300 Winchester Magnum in my 30/06.
This is more of a cartridge size, but you may see something like 7.62 x 51mm, which you will find stamped on the rim of the case, and this means the bullet is 7.62mm and the case is 51mm long. What else is the same size? The commercial .308, which is just a .30 caliber. This is actually a 30/06 cut down. This has even been considered by Sporting Arms and Ammunition Manufacturers’ Institute to be a plausable substitute to shoot in a .308 rifle!
Another common round that has a mm equilivent is 5.56 x 44 mm NATO = .233 except the pressures are different, so you should not want to try it. Another is .303 British at 7.7×56mm, or the 30/06 Springfield which is 7.62x63mm.
Here is a quick MM to inch equivelancy chart.
Another Chart showing comparisons, I admit that I took from Wikipedia:
If you see something with Magnum, Super, or Special in the name, it doesn’t really mean anything. All it means is that the manufacturer created a cartridge that they thought had good power and they wanted to market it that way. So a 300 Magnum, really just means that they made a .30 Caliber with extra charge (powder) to give the bullet a much higher sectional density (which I will talk about soon enough), and then they named it Magnum so you will buy it.
Interestingly enough, while I am on the calibers, I should point out that the .38 Super and .38 Special are not actually .38. The bullets for a super are actually .355 and the special are .357. So why are they called .38 then? Well, I am glad that I asked for you. These were created in a time that many rounds were made just like the .22. That is the bullet and case are essentially the same width, so they measured by the width of the case. So even though the bullet is not .38, the case is. These are just an exception to the rule.
Hope I cleared things up instead of muddying the water. Before I let you go, I want to send you to a Wikipedia page that will send to the correct page for ANY rifle ammunition question you may have (as long as you know the bullet specifically.)
Enter the challenge for: