I have been playing with Carcanos off & on for years. Before I shoot any of them, I slug the bore. If you do not know how to slug a bore, a gunsmith can do it. Usually does not cost much, & most will do it while you wait. That would be my advice if you want to be sure.
Slugging the bore is now habit with me on any milsurp. I used to pay a gunsmith to do it, but it is so simple I do it myself.
I have never achieved great accuracy using the .264 bullets. It is with the 268gr Hornandy bullets that make my Carcanos tack drivers.