A "ken" is not a widely recognized unit of measurement in modern systems. However, the term "ken" is more commonly used as a noun or verb in English and has a different meaning.
As a noun, "ken" refers to one's range of sight, perception, or understanding. For example, you might say, "Beyond my ken," to mean something is beyond your understanding or knowledge.
As a verb, "ken" means to understand, perceive, or know. For instance, you might use it in a sentence like, "I cannot ken the complexity of this issue."
In these contexts, "ken" is used to describe one's ability to perceive or comprehend something, rather than a unit of measurement. If you have a specific context in which "ken" is being used as a unit of measurement, please provide more details, and I'll do my best to assist you further.
"Caliber" is a term used to describe the internal diameter or bore of a firearm's barrel or the diameter of the projectile (bullet) it fires. It is typically expressed in either inches or millimeters, depending on the measurement system used.
In the United States, caliber is often expressed in inches. For example, a firearm with a bore diameter of 0.30 inches would be referred to as having a ".30 caliber" bore. Similarly, a firearm with a bore diameter of 0.45 inches would be described as having a ".45 caliber" bore.
In many other countries that use the metric system, caliber is expressed in millimeters. For instance, a firearm with a bore diameter of 9 millimeters is referred to as having a "9mm caliber" bore.
Caliber is an essential specification for firearms because it determines the size of ammunition that can be used with a particular gun. The ammunition for a firearm must match its caliber to function safely and accurately. Different firearms are designed to use specific calibers of ammunition, and it's crucial for firearm owners to select and use the correct ammunition for their guns.