The alloy needed for water hardening, is antimony/lead and just a tich of arsenic. The
inclusion of arsenic is absolutely necessary for hardening to take place.
Alloyed lead shot has enough arsenic, and so do the old style lead alloy wheel weights.
Bullets/balls cast in those, can be hardened to brinel 34, the same as dead soft copper.
Linotype metal is brinel 21, while monotype is brinel 24. High Speed babbet is 28, iirc.
Post hardening working of the hardened bullets(such as sizing,) softens them again. If
sized and lubed immediately after hardening, they will remain hard. It takes them up to
12 hours after quenching, to harden fully. Properly hardened just straight WW bullets can
be driven to excessively high velocities, if the lube is up to it.
Tin/lead mixes will not harden. Tin detracts from the hardening process of the whole alloy.
Just in case you didn't know, but were curious.
Info from: "Jacketed Performance with Cast Bullets", by Veral Smith.