Other than the relining the barrel and chamber along with figuring out the magazine feed and the fact that the Carcano uses a one piece bolt with a head that's a fair bit larger than .223/5.56
The major issue is the fact that maximum pressure of the 6.5 Carcano is about 41,000 psi vs. the maximum pressure of .223 Remington at about 55,000 psi and 5.56 NATO goes up to about 58,000 psi. That's a healthy jump in pressure!!!!
The major issue is the fact that maximum pressure of the 6.5 Carcano is about 41,000 psi vs. the maximum pressure of .223 Remington at about 55,000 psi and 5.56 NATO goes up to about 58,000 psi. That's a healthy jump in pressure!!!!