Caliber measurement question

Basically, the number is always the diameter of the bullet. .380, .45 are in inches, 9mm, 10mm are in the metric system. Simple as that. Some calibers have several "names", .380 for example is also known as "9mm short", "9X17mm" and so on. It has the same diameter as a regular 9mm bullet (AKA 9mm Luger, 9x19mm) but it's a couple of milimeters shorter (the casing is shorter).

Here's a Wikipedia article with some basic bullet caliber info: Caliber - Wikipedia, the free encyclopedia

 

most european ammo is listed by bullet diameter then the cartridge case lenght. the cartridge we call the 9mm is actually a 9x19mm. it the u.s. old cartridge were in inch measurements of the bullet first, then the black powder charge, then the bullet weight, example 45-70-500. 45 caliber by inches, 70 grains of black powder, and a 500 grain bullet.then about 1900 there was an abundance of cartridges in the u.s. and imaginitive names were thought up. 30-06= 30 caliber invented in 1906, 250-3000? =250 bore diameter and the bullet speed of 3000 fps.,just to name a few. then there are the cartridge name that name their round from the bore diameter (270 winchester) while its groove diameter is actually .277".it gets more confusing.any good website will give the cartridge dimentions.and any good website will convert millimeter to inch.hope this helps if you still need help just pm me.

 

The numeric "size" of a bullet is DICTATED by the Manufacturer of that cartridge. PERIOD. For example: a 44 MAGNUM is really a 44 Remington Magnum and the bullet diameter is .429" which is the same for a 44 Special. But the cartridge length determines its designation. This is true with 38 Special and the .357 Magnum.

A 45 Colt also known as : (45LC) is not a 45 ACP which isn't a 454 Casull which isn't a 460 Smith & Wesson. However, they all share the same bullet diameter which is .451" Again, it's designation is set by the cartridge MANUFACTURER for a particular pistol application.

I know this is confising... and it gets worse. For example: 9mm. It "could" be 9mm Luger, 9mm Makarov, 9mm Kurtz, 9mm Largo, 9x17mm, 9x18mm, 380 ACP, 9mm Browning, 9mm Parabellum, ETC. All of which are .355" diameter bullets with varying cartridge lengths... per the Mfg.

I hope this un-coufuses you a little. But after awhile you get used to the designations! REALLY!

 

Here is an Excellent and detailed explaination:

Google Image Result for http://www.sff.net/people/sanders/ammo.jpg

 

The dimensions of a cartridge are set by the inventor. Generally the inventor is a cartridge/gun manufacturer. .44 Smith and Wesson special. .44 Remington Magnum. .45 Colt (commonly but incorrectly called the Long Colt). The numeral designation may or may not have anything to do with the bullet diameter.
The .38 Smith and Wesson special was invented many years ago and .38 "sounded" good even though the bullet was .358 diameter. When the .38 special was elongated and made more powerful, it was called the .357 Magnum even though it, too used .358 diameter bullets. The .357 referred to the groove diameter of the barrel.
When naming cartridges, sometimes the groove diameter is used, sometimes the land diameter is used. The groove diameter is generally .001" larger than the land diameter.
Sometimes the name is a play on the designation of an earlier cartridge. The .38 Super is a hot loaded .38 ACP. The external dimensions are the same, but the pressures are very different.
The .38 Short Colt used a bullet with a .374-.375" diameter in an arrangement similar to a .22 LR (the bullet is the same diameter as the case, called outside lubricatred). This was lengthened and called the .38 Long Colt that used a .358 diameter bullet enclosed in the case (called inside lubricated). The narrowing of the bullet diameter was a result of putting the bullet inside the case. This was again lengthened and called the .38 special even though it still used the .358 diameter bullet. The .38 spl was lengthened and called the .357 Magnum. This was a more accurate representation of diameter but the older, shorter cartridges could still be fired in a revolver chambered in .357. Of course the .357 Maximum came out which took the Magnum term to a never seen before level.
The .44-40 was a .44 caliber cartridge with 40 grains of black powder. It did not actually use a .44 diameter bullet, it used a .427 bullet. The .44 special used a larger .429 bullet but still was not a .44. The .44 Magnum was a lengthed .44 Special and still used a .429 bullet.
To confuse things even more the .38-40 did not use anything close to a .38 caliber bullet, it used a .401 or .40 caliber bullet. It probably played on the public's recognition of the .38 name.

Metric designations generally refer to bullet diameter X case length, both in millimeters. 9 X 19, 5.56 X 45, 7.62 X 39, 7.62 X 51 etc.

Europeans will throw an "R" at the end to identify it as a rimmed cartridge. Some "R" cartridges have rimless sisters. 7 X 57R is the rimmed version of the 7 X 57 (7mm Mauser).

This could go on for days as there are more exceptions than there are rules.

 

Some cartridges are measured on the grove diameter. Like lazeronni and his 7.82 warbird and all others. Just to frig with your head some more.

 

Good responses! You guys cleared up many of the questions I had.

 

There'snothing wrong with a Walther PPK. However, there are a lot of choices out there so look around and try several pistols. You may find another brand and possibly another caliber may suit you better. No doubt 9mm is the most common, but that doesn't make it the best choice! I don't own a 9mm by choice. My preference is .40 S&W and 45ACP in autoloaders, and .357 in revolvers.

 

The PPK or larger cousin PPK/S have a nast habit of slicing tracks into the web of the shooting hand. If you have large or thick hands stay away from them.

The .380 is generally considered to be the absolute minimum viable caliber for defense. Many folks would consider it only for a back up to a "real" caliber handgun of at least 9mm. Others believe the caliber "must" begin with a 4.