>>action smoothness on Carcanos is a BIG variable.<<

Very true. Some of this comes from the roughness of the machining of the ejector slot.

The Italians were a bit too cute designing the trigger and ejector to use the same spring. As a result the spring force on the ejector is kind of high. With a rough bottom ejector slot you can get a very heavy and uneven force required to operate the bolt.

If your bolt set up works smoothly there hardly an action that is smoother or more positive feeding than a Carcano.