Tom,
without a picture it is always difficult.
The C on the primer is typical for factory loaded CBC cartridges.
The exact rason is currently not nown to me.
If the CBC is at the top it indicates a berdan primed case,
at the bottom it indicates a boxer primed case.
If you talk to Patrick Ennis at the Garda An Siochaná - Ballistic Section in Phoenix Park he can certainly help you with the caliber identification. He has CartWinPro
Greetings
Axel