What is the diameter of a 12 gauge rifle slug in caliber?

The diameter of a 12 gauge rifle slug is approximately 0.72 caliber. The term "gauge" in firearms, particularly shotguns, refers to the size of the bore relative to the number of lead balls of a given diameter that would equal one pound. For a 12 gauge shotgun, this translates to a bore diameter of roughly 0.729 inches, which is typically rounded to 0.72 when converted into caliber measurement (1 caliber equals 0.01 inches).

This means that a 12 gauge slug, when measured, typically has a diameter slightly less than 0.73 inches, making 0.72 caliber the most accurate representation of its diameter in terms of conventional caliber notation. The other options, which represent larger diameters, do not accurately reflect the size of a 12 gauge slug and are therefore incorrect.