These guys upload their battles to youtube, where you can see that they have up to 10 shells donated as troops of the alliance
https://www.youtube.com/watch?v=I5FjuNfYaHM
https://www.youtube.com/watch?v=4mn9KODOcKk
http://prntscr.com/iusdcf
http://prntscr.com/iuse17