Actually, they do not have a thicker jacket, it is just a thin layer of copper to protect the barrel from "leading". The copper "jacket" doesn't really do anything to make the bullet hold up better. The difference in them and powerbelts is that powerbelts are pure lead (softer) and the FPBs are a lead alloy (slightly harder).

I do like them though (FPBs). They have killed two elk in the last two years for me.