What is determined by measuring the diameter of a firearm's bore from land to opposite land?

The measurement of a firearm’s bore from land to opposite land refers specifically to the diameter of the bore, which is a defining characteristic of a firearm's caliber. Caliber is typically expressed in either inches or millimeters, and it represents the internal diameter of the barrel. This measurement is critical because it helps in identifying the specific ammunition that can be safely used with the firearm, influencing both performance and accuracy.

Gauge, on the other hand, is a different measurement system primarily used for shotguns and relates to the number of lead balls of the bore diameter that make up a pound. Length pertains to the overall size of a firearm or the ammunition but does not describe the bore diameter. Weight refers to how heavy the firearm is, which again does not have anything to do with the bore measurement. Understanding the distinction between these terms is vital for any responsible hunter or firearm owner, as using the correct caliber is essential for safe operation of firearms.