They are different ways of expressing the same thing. A bullet that is 7.65mm is just that- 7.65 millimeters in diameter. Is the US, we frequently use caliber rather than millimeters- that same bullet was be a .32 caliber- or 32/100ths of an inch in diameter.
metric vs inch measurement
.001 inches. Makes a difference depending on what you are shooting, how old the barrel is, etc..
The .22 caliber bullet is ABOUT .22 inches wide. A .32 bullet is about .32 inches wide. The bullet will also be heavier due to size.
caliber 38 is a caliber 38. bullet dia. is .357 caliber deals with the dia. or measurement around the bullet head, not the bullet case.
They're both measurements of the diameter of the round (or the barrel). Caliber is a measurement in inches, and millimeters are millimeters. For instance, a .30 caliber bullet is 30 hundredths of an inch, or 7.62 millimeters in diameter.
The .22 bullet is smaller than the 9mm in size, (about 6mm) and is lighter in weight.
The main difference between a 9mm and a .45 caliber bullet is the diameter. A 9mm bullet has a diameter of 9 millimeters, while a .45 caliber bullet has a diameter of .45 inches. The .45 caliber bullet is larger and generally heavier than the 9mm bullet, resulting in differences in recoil, speed, and stopping power.
Size and amount of propellant
As far as diameter, there is very little difference. A .357 is .358 in diameter and a 9mm is .356 in diameter.
Caliber refers to the diameter of a bullet (bullet is the part of a cartridge that is fired out of the gun). A .223 caliber bullet is .223 inches across. It is normally used as a rifle cartridge. a .45 caliber bullet is more than twice as wide as a .223, and is usually used in pistols. The .223 is lighter- it weighs about 1/4 of a .45 bullet, and they are different shapes- .223 is usually pointed, the .45 is rounded.
Size and relative power. A .40 caliber bullet is .40 of an inch and the entire cartridge is 28.8 millimeters long. A .50 caliber (handgun) bullet is .50 of an inch and the entire cartridge is 40.99 millimeters long. The .50 caliber has more powder, more velocity, and more muzzle energy.
A .50 caliber bullet is measured by its diameter, which is half an inch (or approximately 12.7 millimeters). Measurement can be done using specialized calipers or micrometers. The caliber of a bullet refers to the diameter of the projectile it can fire.