I have always heat treated all my cast bullets for my 44 mag.
By heat treating in an oven at various temperatures for various time limits, you can customize your bullet to do what ever you want.
For target shooting, I will normally heat treat mine at 450 degrees for 1 hour and drop in ice water. This gives me a BHN hardness of 33-35 with WW metal.
For hunting, since I can push 300gr cast bullets from my 15" contender over 1800fps, I will heat treat as above, and after the bullets are stable, I will then re-heat treat at 250 degrees for 45 minutes and let them air cool. This will draw the hardness back down to around 16-18 BHN, which will have controlled expansion at 1800fps.
The best item to get is a book titled "Jacketed performance with Cast Bullets" by Veral Smith. He is a custom die maker and has compiled a very good paperback going through all the particulars and recipes for making cast bullets and how to get them to perform their best for your needs.
Hope this helps a little.
