In past years there have been reports of S&W revolvers with original type barrels that failed to mate up with the frame, and since the introduction of the new Colt Cobra and King Cobra a couple of reports of barrels not mating up.
In all cases this is a cosmetic fault, the revolvers shoot well and there are no reports of barrels loosening.
If the owner of the King Cobra sends it back to Colt for warranty repair they'll reset the barrel correctly.
Have him contact Colt for a return label or pickup.