I'm a casting tragic, hundreds of molds, hundreds of cast boolits, tens of handles and tens of cast bullet 'shooters to keep the whole show running.

Lately, I started to look at mold material, why when I cast multiple boolits, I always cast with all steel, all brass, or all aluminium and not a mixture of mold metals.

If using an aluminium mold with alloy at a temperature that will 'fill out' a steel mold, the aluminium mold will start to throw boolits that are 0.001" to 0.002" larger than when using an alloy that will just cast good boolits in aluminium but will cause wrinkles in a steel mold.



Similarly an all brass mold can be used to cast larger bullets by using an alloy at a hotter temperature (i.e. cast steel) due to the co-efficient of thermal expansion of different mold metals.



All this is very useful to the modern caster by allowing him to control boolit diameter and even tightning the fit of gas checks upon the boolit base.