A lot of calibers can use the same shell holder. For example among the calibers I load; .45 ACP, .22-250, 6mm Rem, 6.5x55, .308, and .30-06 all use the same shell holder.
.380 will generally use the same shell holder as .223/5.56.
FYI, Lee dies come with shell holders and are ususally a bit less expensive than RCBS. No quality complaints either.