A variety of ingots added to the pot during batch production account for the running variance. Wheel Weight ingots have a large variance and frequently contain much more than Lead, Tin and Antimony. The use of a mass spectrometer gives the exact composition of the alloy, but a mass spectrometer is a difficult tool to access!
As an aside, the light weight bullets are hard relative to their lead alloy counterparts. I do not have a good scientific way to non destructively measure the hardness yet. The 45-70 light alloy is very frangible upon impact. A topic for another day.
I did not notice a width change but that may be because I quench and age the bullets for a month and then size them. I did not measure for a change in length but I may start. The OAL of the cartridge was correct in the end.
I considered writing an article for TFS but I don't know if there is any interest.