Funny you should ask! As a matter of fact they're sent to a secret mountaintop convent in the Austrian Alps where the cloistered Lithuanian refugee nuns completely rework them, fabricating new parts as needed, remanufacturing the entire firearm. Then they're shipped to the Vatican in Rome where they are fully proof tested by a blind Monsignor casualty of WWII who test fires each gun for 1,000 rounds in a specially designed state of the art shooting range located deep in the catacombs and equipped with custom aural feedback targets which describe the exact ballistic performance, trajectory and target point that is impacted. Once they pass his rigorous testing they're dismantled and cleaned, blessed with holy water and given to the Pope's own private Vatican Guard.
That's where the saying comes from, 'NUN BETTER THAN A CZ!' in case you didn't know...