Theres a bit of a trick to it. I learned it from a buddy of mine who does not belive in heat treating at all. He shoots a lot and casts even more.
You don't need that flux .
weigh the antimony ,Melt the antimony at all 1200f. All will be glowing red!
add warmed pure lead to make a 50/50 mix. (as soon as you add the lead the antimony will re freeze, but will remelt in a wile.)
Now mix,mix mix,flux with normal flux, and pour your ingots with a heavy dose of mixing all the wile.
Now you have 50/50 rainbow looking ingots that will melt with ease at much much lower temps when you alloy.
All my alloy comes out even and no grainy feel.
Hope this helps. ....buck