Caliber Conversions Table - Manuel Lisa
Caliber Conversions Table
By Matthew J. Boyd
| |
|The purpose of this conversion chart is to give you a rough idea of how the bullet diameters compare to each other. It is meant as|
|a quick reference for when you're not sure how the different measured sizes relate. Or, for when you and your buddy are having a |
|debate (9mm vs. .38 caliber, for instance). |
|Just because a .30 cal bullet is the same nominal diameter as a 7.62mm bullet does NOT mean that you can interchange the bullets |
|in firearms chambered in those sizes. |
|Cartridge length seriously comes into play when you start looking into making custom ammunition or switching similar bullets and |
|brass around. You can NOT take a cartridge that is 2.5" long and expect it to cycle properly in a firearm that is chambered for a |
|2.4" long cartridge. If you try to do that, you will put yourself and others at risk. Or, you'll just look like a dummy when you |
|have to have someone take apart your gun and un-jam it for you. |
|I made the mistake as a kid once and grabbed the wrong cartridge for a friend's .30-30. I did get the cartridge out safely, 3 |
|hours later, after disassembling and reassembling the whole carbine. |
|Not all calibers accurately reflect the actual size of the bullet. Just like the marketing department to make sure that not all |
|things are exactly as advertised. It's their job to bend the facts, take advantage of different types of measurements, and to |
|confuse the average consumer while making company X more money in the process. Some calibers are named for the bore diameter, and |
|some are named for the actual bullet diameter. Some are overestimated or rounded up to make them seem like a more powerful |
|cartridge, or rounded down to have an even number. I'm sure, for example, that the famous .44 Magnum wouldn't have been so cool if|
|it had been named the ".42 Magnum." |
|DO NOT try switching bullets around. Attempting to switch bullets of like calibers in different cartridges can be dangerous. Too |
|large of a bullet can cause cycling problems, jams, or excessive pressure buildup. Too much pressure can cause a barrel to explode|
|injuring the operator as well as nearby people. Too small of a bullet can cause cycling problems, or cause the bullet to rattle, |
|rather than scream, out of the barrel. Make sure you have a micrometer to measure the true diameter of the actual bullet. |
|Formulae |
|1 inch = 1.00 Caliber = 25.4mm |
|Caliber x 25.4 = size in mm (Example: .45 caliber x 25.4 = 11.43 so .45 caliber = 11.43mm) |
|Metric designation / 25.4mm = size in Caliber (Example: 9mm / 25.4 = 0.35433 so 9mm = approximately .35 cal) |
|When dealing with calibers that have hyphens in them, discard the hyphen and the number after it. The number before the hyphen is |
|the caliber of the bullet. The number after the hyphen often refers to how many grains of gunpowder was once used in the |
|cartridge, or the year that the cartridge was made. (Example: .45-70 = .45 cal with 70 grains of black powder.) |
|Terminology |
|Brass - The cartridge case. This is usually made out of brass, hence the name. The case holds the powder inside, a primer in its |
|bottom, and a bullet in its mouth. Assembled, these components constitute a cartridge. |
|Bullet - The projectile that is propelled downrange when a gun is fired. Bullet cores are usually made of lead that is often |
|jacketed or semi-jacketed in copper or a copper alloy. Or not jacketed at all (a.k.a. cast or swaged lead bullets). |
|Bullet diameter - The actual diameter of a bullet, usually measured in decimal fractions of an inch (.308"). In Europe bullet |
|diameters are typically expressed in millimeters (7.62mm). In recent years many cartridges have been named for their bullet |
|diameter (.308 Winchester). |
|Bore diameter - The land to land diameter of the inside of a gun barrel, usually expressed in decimal fractions of an inch (.300).|
|Traditionally cartridges have been named for the bore diameter of the guns that fire them (.270 Winchester). |
|Cartridge - The combination of the bullet, case, powder, and primer in a ready to fire configuration (the way you would buy them |
|in a box from a store). |
|Case - The case is really a vessel that holds the powder inside, a primer in its bottom, and a bullet in its mouth. It is usually |
|made of brass. Assembled, these components constitute a cartridge. |
|Firing pin - This is a small metal rod inside of a firearm that strikes the primer of a cartridge when the trigger is pulled and |
|it is hit by the hammer. This causes the primer to ignite the powder inside the cartridge and propel the bullet out of the |
|firearm. A long, heavy firing pin that is propelled by a stiff spring rather than being hit by a hammer is usually called a |
|"striker." |
|Groove diameter - The groove to groove diameter of the inside of a gun barrel. This is usually the same as the diameter of the |
|bullets that it is intended to fire. |
|Primer - This is a small cap that fits into the rear of the brass. This cap usually contains a highly sensitive explosive that is |
|required to set of the powder inside of a cartridge. |
|Smokeless Powder - The nitro-cellulose based gunpowder that is used in most modern firearms. There are several manufacturers of |
|smokeless powder and numerous individual types of smokeless powder. Among the best known brands in North America are Alliant, |
|Hodgdon, IMR, Norma, and Winchester/Olin. |
|Striker - A long, relatively heavy firing pin that is propelled by a stiff spring rather than being hit by a hammer. |
| |
|Common name |
|Bore diameter (inches) |
|Bullet/Groove diameter (inches) |
|Bullet/Groove |
|diameter (MM) |
| |
|.50 cal |
|.500" |
|.510 |
|12.954 |
| |
|.475 cal |
|- |
|.475 |
|12.065 |
| |
|.45 cal rifle |
|.450 |
|.458 |
|11.633 |
| |
|.45 revolver |
|- |
|.454 |
|11.531 |
| |
|.45 revolver |
|- |
|.452 |
|11.480 |
| |
|.45 ACP |
|- |
|.451 |
|11.455 |
| |
|.44 Mag. |
|- |
|.429 |
|10.896 |
| |
|.416 cal |
|- |
|.416 |
|10.566 |
| |
|.41 cal |
|- |
|.410 |
|10.414 |
| |
|.40cal/10mm |
|- |
|.400 |
|10.160 |
| |
|.375 cal |
|- |
|.375 |
|9.525 |
| |
|9.3mm |
|- |
|.366 |
|9.300 |
| |
|.35 cal rifle |
|.350 |
|.358 |
|9.093 |
| |
|.357 Mag |
|.38 Spec |
|.350 |
|.357 |
|9.067 |
| |
|9mm, .380 |
|.357 SIG |
|- |
|.355 |
|9.017 |
| |
|.348 cal |
|.340 |
|.348 |
|8.839 |
| |
|.338 cal |
|.330 |
|.338 |
|8.585 |
| |
|.33 cal |
|- |
|.333 |
|8.382 |
| |
|8mm |
|.315 |
|.323 |
|8.204 |
| |
|.32 Special |
|.313 |
|.321 |
|8.153 |
| |
|.32-20 cal |
|- |
|.312 |
|7.924 |
| |
|.303 cal |
|7.65mm |
|.303 |
|.312 |
|7.924 |
| |
|7.62x39 |
|.300-.303 |
|.311 |
|7.899 |
| |
|.30/.300 cal |
|.300 |
|.308 |
|7.832 |
| |
|7.5mm |
|- |
|.295 |
|7.500 |
| |
|.28 cal/7mm |
|.275-.276 |
|.284 |
|7.213 |
| |
|.270 cal |
|.270 |
|.277 |
|7.035 |
| |
|.26cal/6.5mm |
|.256 |
|.264 |
|6.705 |
| |
|.25 cal |
|.250 |
|.257 |
|6.527 |
| |
|.243/6mm |
|.236 |
|.243 |
|6.172 |
| |
|.22 cal |
|.218/.219 |
|.224 |
|5.689 |
| |
|.20 cal |
|- |
|.204 |
|5.080 |
| |
|.17 cal |
|- |
|.172 |
|4.368 |
| |
|BB |
|- |
|.177-.180 |
|4.495 |
| |
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