Nothing replicates metal better than metal IMHO. So if you're talking about a white metal figure with 'lorica segmentata' amour, forget the paints and instead just buff it up to high sheen before adding some subtle dark oil washes (raw umber / vandyke brown etc.).
If it's a resin figure, my current paints of choice for armour are Dark Star acrylic paints - specifically 'Steel' with some 'Old Silver' mixed in - followed by the aformentioned oil washes. Then once the oils have thoroughly dried (give it several days), highlights applied as & where needed using the same acrylic mix (adding a touch more Old Silver) drybrushed on (very dry though!).