That is a 2 cavity bullet mould. It looks like a Lyman. Anyhow, google for the forum "Cast Boolets", many bullet casters there to help you. I am uncertain whether or not moulds are made for the 410 slug, but perhaps a .44 (measures .429") bullet could be used, or a .41 magnum, or .40 caliber bullet will fit. I don't know the diameter of a 4.10 slug, you see.