You have a favorite lead/tin/antimony mix, but then the availability of one of the component alloys you use changes (like has happened to me in the case of lead wheel weights). What do you do now?
A video explaining this utility can be found here:
Well, you can use different alloys if you know how to recalculate the mixtures based on the new alloys. I have made this Bullet Alloy Calculator to solve that problem.
The calculator can be loaded using Excel or the free app from Google called "Sheets". It's very intuitive to use but, that said, it probably doesn't hurt to see a demonstration of it in use here:
https://youtu.be/N2iJBPVaoCU