How about printing replacement parts for the body?
http://www.bbc.co.uk/news/technology-16906549
Or blood vessels?
http://www.bbc.co.uk/news/technology-14946808
As far as guns, makes me wonder if in the future you will have to order a gun and then wait for it to be shipped. Imagine a FFL having one of these printers, the FFL being connected to the gun designers system and the FFL printing your gun. The FFL, being connected to the designer's network, would get a serial number from them and it would be logged into their database. An invoice would then be sent, electronically, and before the FFL releases the gun, you have to pay for it.
Such a printer would have to be able to print various metals and polymers.