you can tell if its copper or zink by the weight, however in the condition its in it has no numismatic value either way, they made over 6 billion. Hoopster and claw are experts, I promise they would tell you if you had a nice find.
Your original pic is good enough to see that its a damaged coin. It absolutely IS NOT a RPM or OMM. Spend some time doing some research on variety vista and wexlers doubled die site, and you'll understand why this isn't a RPM
Better Pictures are not going to help. It's damaged. You are proposing that a Denver minted coin was shipped to SanFran and reminted? or a Denver minted die was RPM'd as an S, or vice versa? I'm confused by your proposed alternative from it being damaged ? As Hoopster mentioned, understanding the minting process (which is very long, tedious learning experience) can teach one a lot of what is and isn't an error versus damage.
from the other heavy strikes it has had, it's probably a copper. The large indent and moved copper in the middle of the bust shows depth to the copper (other wise probably ripping of the copperplate and zinc showing), not the 8 micron thin plating with zincolns.
Welcome to CT. PS - you should only handle coins by their edges or you'll quickly devalue any coins you find with nasty finger prints.
As others have said, it is just post-mint damage (PMD). You might want to save the link below which explains how the Philadelphia Mint makes dies, coins, proofs, etc. There is a list of these other topics along the right-hand side of the page, "Philadelphia Mint Article Series". http://www.coinnews.net/2013/09/13/how-the-philadelphia-mint-makes-hubs-and-dies-to-produce-coins/ Chris
