What a four-pounder’s number describes

Does a cannon’s pounder rating describe the ball’s approximate size rather than its actual weight?

It describes the approximate weight of the solid round shot, with limited variation that cannot turn a four-pound ball into a six- or eight-pound one.

A four-pounder was intended to fire a solid ball weighing roughly four pounds. Manufacturing variation existed, especially among large shot, but a small ball weighing six or eight pounds belonged to a different gun class. Because weight rises with the projectile’s volume, apparently modest differences become significant at small calibres. Period armament lists therefore need to be read with the distinction between bore, projectile diameter, and nominal shot weight in mind.