There were a couple issues on some new Pythons...not even a majority from most reports. Some had poor machining on the muzzle crown...some had loose screws...some would have occasional misfires with certain brand ammunition rounds...some would not advance the cylinder. The problems have supposedly been addressed and corrected by Colt. There may still be some not yet corrected. None of these problems should have happened but they did and from all reports Colt is stepping up and making things right.
I have one of the new 6" Pythons...extraordinary revolver as it's extremely accurate and looks great with no quality control issues at all. I wouldn't hesitate to buy one.