Looks like you have brought up the BHN a bit. Exposing the lead might provide a better test.
Plating bullets usually create heat that softens the alloy a bit. "Bonded" bullets usually also expand/obturate easier due to the same priciples. It also softens the plating metal.
Water quenching any lead alloy will make a harder finished product than most age hardened bullets, period. It will be even harder if its compared to one subjected to heat and forming, one reason linotype varies in hardness not only by alloy, but also by how often it has been "used" in typset.
"Heat treating" isnt in this classification, IMO.
