And rifles and handguns the diameter of the bore usually indicates what?

The diameter of the bore in rifles and handguns typically indicates the caliber of the firearm, which is a measure of the internal diameter of the barrel. This measurement is often expressed in either millimeters or inches, and it helps determine the size of the ammunition that can be used. A larger bore diameter generally corresponds to a larger caliber, which can affect factors like stopping power, recoil, and the intended purpose of the firearm.