What term refers to the diameter of a projectile at the bourrelet?

The term that refers to the diameter of a projectile at the bourrelet is "caliber." In firearms and artillery terminology, caliber specifically indicates the internal diameter of the gun barrel or the diameter of a projectile that is intended to be fired from that gun. The bourrelet is a raised area on the projectile that stabilizes its flight when it travels down the barrel, and measuring the diameter at this point is critical for ensuring proper fit and alignment within the weapon system.

Understanding caliber is important in the context of ammunition specifications, as it directly affects factors such as accuracy, velocity, and the type of barrel required. The term's relevance extends beyond just the projectile itself; it also helps in identifying compatible ammunition for each firearm type.

In contrast, the other terms listed do not accurately define the concept being asked about. "Grain" refers to a unit of weight commonly used to measure the mass of a firearm projectile, while "bore diameter" describes the interior diameter of the firearm barrel itself, which may not necessarily correspond to the projectile's diameter at the bourrelet. "Caliber number" is not a standard term and could lead to confusion; it might suggest a numeric representation of caliber but lacks the clarity and specificity of simply