WHAT DOES CCI SIZE 11 PERCUSSION CAPS MEAN?

I acquired a plain optima, not an elite, about 6-7yrs back. I attempted a variety of brands of primers in it. I could about six rounds through the typical CCIs or Win magnums and then the primers would get packed in with carbon. They were being very difficult to extract! With most other models 2-3 photographs would demand tools for getting them out