For example, why 5.56mm and not just 6mm? Why 7.62mm instead of just 8?
In: Technology
Because they’re often based on commonly used Imperial bullet sizes. 5.56mm is approximately 0.22″, for instance, while 7.62mm is 0.3″.
Caliber is an imperial unit of diameter measured in 100ths of an inch.
So .25 caliber is 1/4 inch and .50 cal is 1/2 inch.
Why then is a bullet measured .310 called .303 british? I dont know.
So why not whole numbers? To differentiate them. For example 7.62 Argentine, 7.62x54r, 7.62×39 Warsaw, 7.62 Nato. Absolutely none of these bullets are interchangeable. Naming conventions! Helpful.
is this a serious question?
Ok so the simple answer here is that there are just too many incompatible cartridges to not have more numbers available. If you rounded everything close to 8 to 8 then you’d have many cartridges that wouldn’t fit or be dangerous in the wrong gun all called 8.
I can’t think of any off the top of my head but some cartridges were “misnamed” from their actual bullet diameter because that number was already taken and the goal was to avoid confusion.
It’s not all that standardized. Some measure diameter of barrel, some measure diameter of the bullet, some are rounded to the thousandths, some to the hundredths, some purposely use a different number to differentiate themselves from a same diameter bullet.
Some are. There are both [6mm](https://en.wikipedia.org/wiki/6_mm_caliber) and [8mm](https://en.wikipedia.org/wiki/7.92%C3%9757mm_Mauser) bullets, loaded into a variety of cartridges. Cartridge and projectile design is complicated, with each iteration designed to perform in a specific way and fill a specific niche.
There are tons of calibers and they vary greatly. But sometimes it’s that stuff is designed with the inch measurement in mind and sometimes it’s not. There are some that are whole numbers in the metric system, for instance the 10mm pistol round. Which BTW a shortened version of the 10mm is the 40S&W.
Another thing is that sometimes a particular size is just better suited for a weight and ballistic coefficient. When you start looking at rounds that will be used at a longer range that makes a huge difference.
[https://en.wikipedia.org/wiki/Table_of_handgun_and_rifle_cartridges](https://en.wikipedia.org/wiki/Table_of_handgun_and_rifle_cartridges) gives a listing of a lot of the major rifle and pistol rounds. The older it is the more likely it is to be of an inch variant and newer stuff that is designed to use an existing bullet will be as well.
Also a lot of times it’s just in a name. Can’t have 10 different callibers that all are 10mm now can we. So we can call one a 10mm, one a .40 and another a 10.1mm and they can all use the same bullet but technically be a different round.
The precision is required.
Attempting to use 5.45 in a 5.56 gun (or vice versa) could end very badly.
There are some very good explanations of bullet development, but I feel like the simple answer is similar to why we don’t say that a 5’10” (or 1.778 metres) person is six feet tall (or two metres):
It’s not accurate.
Bullet design is all about achieving the best results, be it velocity, penetration, stability, wound profile etc.
Designers don’t go ‘lets make a good 8mm bullet’. They start with a design criteria and find the best size for those sets of criteria during development.
Latest Answers