Try to find the new (4th) edition of Lyman's Cast Bullet Handbook
. First 15 chapters written by Mike Venturino. Robert Block, PhD seems to have a pretty good handle on the metallurgy side of casting. Other excellent articles as well.
If you get serious about casting for that 45-70 and have a Sharps that needs feeding I'd spend some time with Venturino and Garbe's book on the subject.
In case nobody mentions it there's quite a bit of good material out there on the subject of casting. Read all you can, we'll tell you where to find more.
Stickies here are excellent as well.
I've only been casting a few years and I still get excited every time I plug in the pot. Hope you enjoy it as well.