Starline cases are empty brass cartridge cases used for reloading.
This is most likely what is meant when referring to “Starline .30 cases”
There are several “.30” cases:
The Tokarev case looks very similar, but using the wrong load data can cause problems
✔ High-quality brass ✔ Long lifespan (multiple reloads) ✔ Consistent thickness and dimensions ✔ Available for rare calibers