Sitka,
Mmm. As I originally understood Ken, he was interested in the formula to determine the density (or SG) of a bullet with unknown composition (alloy, jacketing, etc) I assume that he wanted that value in absolute terms and therefore the displaced water volume (i.e. volume of bullet) is simply the difference between the two mass measurements. Therefore, if the bullet mass is simply divided by the volume the density is obtained directly.
If we perform the exercise in SI units, then the calculation of SG is moot (since the reference density of water at 4 C is 1 kg/L) and the density is simply equal to the SG. However, working in units other than SI one would have to ensure proper conversion factors...
