There still is a scarce supply, so C555 bats tend to be a out of stock often. Sc500 is Easton's designation for the alloy used for the aluminum shell in the Easton Z-Core. This is probably the most significant change in alloy design for a softball bat since the introduction of C405 back in 1996. This alloy was developed jointly by Kaiser Aluminum and Ashurst Technology for exclusive use by Easton. What is so special about this alloy is the presence of a dilute Sc addition.
Scandium is a very rare, expensive, and lightweight metal.
When added to Aluminum in dilute quantities it is responsible for increased strength from Al3Sc precipitation, enhanced weldability, and significant resistance to recrystallization. This alloy also has a carbon fiber wrap inside the barrel for durability. Sc777 is the brand new alloy exclusively from Easton. It is similar to the SC500 above with stands of titanium in the core for more durability and a bigger sweet spot. We will update this information as soon as we know more about it.