Sensop: I added numbers to your questions, for reference. Some of ther following might be helpful.
1.What are the most widely used methods of lead bullet tempering?
2. For lead, does tempering = hardening?
3.How did grandpa do it? (Are there old methods vs new methods?)
4.How deep into the lead alloy, does the hardening take effect?
5.How much of this hardening does resizing remove? (i.e., how much of the bullet is
typically removed by the sizing die?)
6.Recommended literature for my education on this (besides Lyman, of course)?
1.Dumping the cast bullet into a bucket of cold water is one way, and if I recall correctly, reheating cast bullets in an oven, to a point just shy of their "slumping", then dumping into cold water, is another.
3.He may well as fired them "as cast", after lubricating them, of course.
4. Don't know.
5.Supposedly, the sizing die used should not resize the cast bullet more than a couple of thousands, say size a bullet with as cast dia of .310, down to .308"dia. Again, if I remember correctly, you would resize your cast bullet, without lubrication, BEFORE heat treating (hardening), then lube them.
6. Lyman is likely one of the best places to start for information, though The NRA has likely poublished some technical articles on various aspects of casting, paper patching and hardening. You might also consider a harder alloy, such as linotype, but only if you really need it.
The foregoing based on some stuff I have read, over the years, as well as data obtained by asking "dumb" questions. I do not myself, cast bullets. Don't have a proper place to do it. Looking at what I pay for good cast bullets, buying the equipment and materials necessary, isn't worth while as I see it.
Hope the foregoing helps.