Need help. Noob To casting, 460 sw magnum

Hello guys,
So i need some help. After doing quite a bit of research online for the last several weeks I am seeing mixed data, and I really need some guidance as I am new to Casting. So I realize now it probably would have been easier to get some Roto metal, but that's not an option right now, so what I did purchase was pure lead pure antimony and pure 10 because my original intent was to create my own alloy at whatever bhn I needed it. There is really only a few calibers I'm interested in casting for, first and foremost being 454 Casull and 460 Smith & Wesson Magnum. I do have xtp mags Etc and have already loaded some of those but they are expensive and so I want to cast my own. I have a Lee 300 grain .452 rnfp mold I believe. I also have a Lee hardness tester. And I plan on Powder Coating . What are your suggestions for my bhn particularly for the 460 Smith & Wesson, and will water quenching increase that? Will all the bullets need gas checked for that gun if I powder coat and or have the correct BHN? And what are your suggestions for my lead to antimony to tin mixture?

😊 thanks