Not enough information! Weight of hammer, type of hammer, what is the surface of the anvil composed of?
Let's see. Cup has a compound that is sensitive to shock and is hit with a hammer. This ain't rocket science!
My advice is for you to stay away from handloading tools of any kind and sharp objects.


Shew me thy ways, O LORD: teach me thy paths.
"there are few better cartridges on Earth than the 7 x 57mm Mauser"
"the .30 Springfield is light, accurate, penetrating, and has surprising stopping power"