Upon releasing between the cavity and core side of zinc alloy mould, any casting parts would inherit a parting line on its surface.  This parting line is inevitable, even deploying the most sophisticated machinery during the tooling process could not guarantee a complete smooth surface, in most cases, a very tiny hair size parting line would still be visible to naked eyes.  As mentioned previously, zinc alloy casting part would require polishing to remove flashes (substances spilled out from the mould contact surface due to high pressures).  During the polishing process, however while attempting to remove flashes around the parting line, it could easily cause unexpected damages, in worst case the round surface would be distorted.

To achieve a more authentic gun barrel surface smoothness, Waltersons bought aluminium tubes with larger diameter and using precisely lathe machine driven by Computer Numerical Control programming system, known as CNC slowly trim down the tube diameter into desire size, even though this technique incurred a higher manufacturing cost compare to traditional casting, the extra effort would be highly appreciated by collectors in the end.