Keep in mind that there is still a wide range of alloys that might be used for casting. Lead for rifle bullets will be harder, pistol softer. Some people cast pure linotype for rifle bullets. Plus if you powder coat you can get away with softer lead than otherwise.
Kind of an art as much as a science. For example, I have some ingots that are pure lead. I have some ingots that are wheelweights. I have some linotype. When I cast for pistol use at low velocities, powder coating, I mix a certain number of pure lead ingots with a certain number of wheelweight ingots to get to the hardness I want. If you want to just lube them, then wheelweight lead is just about perfect as is. I think I mix my pistol bullet, powder coat intended alloy at 5 WW/4 pure typically.
If you have any idea on whether the intent was rifle or pistol use it will point you in the correct direction. You can get a lead hardness tester if you desire, or just try a few out and see how they work. A range of pencils can even be used to test lead hardness as well. Or cast a few bullets and mail them to someone with a tester. You get the idea.