As a former zealous Calvinist, I can tell you that Calvinists do not reject “free will”.
Calvinists believe that we make real choices according to our desires. In that sense, the will is indeed free, because we never are forced by God to make a choice contrary to our desires. We indeed always choose what we want most, in any given situation.
Now… While I don’t know of (and don’t have the time to find) anything supporting it in the CCC, I would bet that the CC affirms that we “are never forced to make a choice contrary to our desires”, and “we always choose what we want most, in any given situation.”
Some (and I think not all) Catholics-- like some protestant schools (Arminianism, Weslyanism), would argue that the will is not free unless one is free to “choose what they do not want”. To me, this is nonsense, but it is a widely held definition of free will.
My point though, is that the difference between Calvinism and Catholicism does not hinge on free will. For that matter, Catholics do not differ – at least not with mainstream Calvinists-- on the question of predestination (which all Calvinists believe is unmerited and most believe applies only to the elect and heaven) or reprobation (which most Calvinists believe is merited by sin). Neither do Calvinists disagree that Christ’s work is sufficient for all… and Catholics do not disagree that Christ’s work is only “actually finally effective” in saving those who believe till the end.
There are largely only two key differences between Catholic and Calvinist thought (insofar as the economy of salvation and gospel is concerned):
- Whether God’s grace is efficacious in all cases to bring anyone who is graced all the way through to glory-- i.e., can a true believer ever walk finally away from God unto damnation (or rather, will God ever let him do so).
- Whether God elects those he first knows (/sees/foresees) as having faith to the end, or if he elects persons without regard to (i.e., logically “before”) consideration of any foreseen faith.