It is my understanding that either nickel or copper are solid lubricants used to prevent bridging and binding as shot transitions thru the forcing cones. Hard shot doesn't deform either upon acceleration or forcing as easily as soft shot. All the bagged shot I have ever seen is graphite coated for the same reason at less expense than plating of whatever thickness. If you plate soft shot it still deforms just maybe not as much as unplated of the same alloy. Both hardness (alloy) and lubrication matter. The real issue is how much are you willing to pay and in what volume of consumption.
