Hi Otto--
Do you know the bore dimension in your rifle? Mine is larger than .264, but shoots the .264 160 Hornady fine and doesn't have accuracy trouble with 140 gr. SP Hornadys, let alone tumble the bullet. It definitely doesn't feed the 140 as well. I still maintain that Curl should start with the .264 RN and see how it works, holding the Carcano bullet in reserve as a fallback. That said, thanks for posting on your experience--the great thing about the 'net is the ability to share with the rest of us, and all of this trial-and-error helps!
Best,
Malcolm