4 to 6 days seems like an awfully generous estimate of delivery time for Registered Mail for the distance and this time of year.
Registered Mail is actually Priority Mail with the added security of the sign off at each handling point (that's the Registered part along with the added value insurance). Mail never goes a direct route, lots of indirect routes to resorting centers and the like. The last registered package I sent took 15 days betw NY and Missouri,,and they didn't trax that one either. Everyone has what they consider the 'best way to go' in shipping a firearm. That's the one way that they themselves have never encountered a problem with. When they do, it becomes the poorest service on earth. Truth be known, they all have problems at some point.