The viability of grain refining phosphorus deoxidised, high residual phosphorus Cu (DHP-Cu) by particle inoculation through the formation of in situ Zr, Ti, Nb, La, Ce, Gd and Nd oxide particles, additions of WC and NbB2 particles as well as additions of Ti+B, Zr+B, Al+B and Ca+B with the purpose of forming in situ boride particles have been investigated under TP-1 casting conditions. Nominal additions of P in the range of 300–690 wt ppm and of Ag of 150 wt ppm have also been explored. In comparison, it appears that it is more difficult to grain refine DHP-Cu by particle inoculation than it is by the combined addition of P+Ag solute elements to a residual content of 396 ppm P and 143 ppm Ag (and having very low contents of Ti, Zr, Al, Ca and B microalloying elements) for the conditions studied.