The Carcano action is equal to a large ring Mauser . The Carcano was not "designed" to shoot the 6.5mm . The 6.5mm round was picked to be used in the Carcano as it did what the Italians wanted at the time . The Carcano is a Manlicher action , made from very good steel . The same action the was used with many other cartridges . I have built many sporters in some high performance cartridges , never had a problem . The problem with the 8mm Carcanos is that they were built post war from used parts with very little quality control . If the rifle is put together correctly , it is fine for 8mm . Also the Vetterli's receiver will not stretch to failure . With rear lugs , the bolt will compress first . Either way the headspace will have increased to the point the rounds will start misfiring .