Thant's because one is bronze and the later one is copper-plated zinc that the Mint did not do a good job on initially when they started. It's just unused pocket change now and weighting down piggy banks. I put down "unused pocket change" because pennies are no longer used here. It gets rounded to the nearest nickel.
Yes.. I weighed them. It’s like an old Lincoln verses a shield (Zincoln). Yes it came from someone’s pocket change.
