The toughest hard bullets one can make are with Wheel weight metal, dropped from a HOT mold into cool water. Full hardness of about 20 bhn will be there within 24 hours. By HOT mold, I mean the bullets should be coming out uniformly frosted.
Linotype, if one has high quality metal, will produce the same hardness when water quenched, slightly less if air cooled. Linotype hardness gradually degrades with time and at about the same rate as water dropped WW bullets. Best way to store to minimize hardness loss in is your deep freeze.
