I started handloading metallic cartridges around 1979. Back then the Sierra manual was popular but it did nothing for me. I purchased small Hodgdon data manual that was good for the recipes but didn't really explain what was going on. A few years later I purchased a very large Hornady manual that had great pics and illustrations that assisted me more than any other had in perceiving the physics of what was happening, brass working, and headspacing.
Load recipes were nice but it seemed I rarely used the projectile specified in the recipes so I always started with minimum charges and worked up and altered seating depths as I worked up a loading for a specific rifle. A change of powder or projectile started the whole process again but I was able to fine a load that a gun liked most of the time.
In the 80's when I fiddled with handguns and blackpowder I began casting actively, working up alloys, sizing to bore, etc. and found the Lyman references handy. But in the end it always took experimentation with the materiels available in the local scrap yards and working up loadings to achieve satisfaction.
Manuals are useful tools but they're not "bibles". Today I wouldn't fool with them at all since so much of the same (if not better) information is available online. A good mentor is the best manual.