It looks like environmental damage. Can you post an image of the edge from 3-6 o'clock? It looks a bit odd.
Acid treated and the edge looks split because the copper dissolved more quickly than the nickel, is my guess.
Now that (never) crossed my mind , guess thats target number two ! My thanks to you , have a happynewyear !
Here's a link: https://en.wikipedia.org/wiki/Hydrozincite When the thin copper plate is split or compromised, it exposes the zinc to the elements.
...rifle ammo costs roughly $1 per round. Are you sure you want to spend that much on a 1/2 cent coin? ...Spark
I agree on the ammo , heres the funny part i inherrited my fathers coin collection , plus the useual trinkets he was remembered for, in the box was a hand full of old .22 ammo , mb he felt the same way , if their not worth it ( their targets ) ! Seriously i think i picked up his ( save it ) gene anything odd is worth the conversation (acid ) that alone makes the coin more interesting Rolls of walking liberty , roll of buffalo nikels, roll of mercury dimes , and several loose silver coins several all diff denominations all of the coins have been circulated some more than others ,