Lead and lead alloy is usually measured with the Brinell scale. It is just a scale to compare different materials. Pure lead is 5, super hard heat treated lead alloy can be as hard as about 30. Typical cast commercial handgun bullets run 11-18, and are a lot harder than they need to be unless you are looking for magnum velocity. The quality of the lube used on a lead bullet has much more effect on leading of the barrel than bullet hardness.
You can do a web search on Brinell hardness and find ratings of various materials that you might be more familiar with.