Thank you rtbcomp, I really don't know the specific type but imagine it's cast aluminium alloy which according to your scale in eng toolbox has around the same melting point temp as aluminium. Thanks again.
First time I poured melted alumin in a mould it cooled with a big recess in the top centre, appeared to contract on cooling, any way to fill this, or is it a case of making the mould longer than needed and cut the bad end off?