The Carcano uses .268". Many a shooter has ruined accuracy (and maybe a rifle) by forcing .264" bullets through .268" bores. Accuracy is terrible; leading or pressure issues may occur.
Safety note: Always consult a current reloading manual and have your surplus rifle inspected by a qualified gunsmith before firing. Many Carcanos and Dutch Mannlichers have suffered from poor storage and may have compromised barrel integrity. 6.5x52r vs 6.5 carcano
6.5x52R, due to bullet diameter compatibility. The Carcano uses