The powerbelt Platinums have the better Jacket that holds the bullet together. With the copper series, its a very very thin plating and is wrapped around soft lead. This copper jacket, splatters when shot at high FPS when it comes into contact with something heavy such as bone. Slowing it down with the charges i recommend, you wont have this problem. Its not that the Platinums are "harder" They offer a better jacket that is supposed to hold the bullet together when driven with higher powder charges.
I plan on buying a few packages and finding out just how much better they are.