They're legal, they can suck a fat one even if you do have them. You can even have the files for a DIAS (but if you print a DIAS and get caught you'll be in prison for 10yr.) You can print guns just fine legally though, but only for you they are not* transferrable.
*There is some contention over whether or not it would be legal to transfer. The law specifies intent which is hard to prove, and lends itself to the "well I intended to build it for me, but then eventually I let go of it when I wanted to upgrade..." argument. Thus far I don't think precedent has been set and I certainly don't want to be the case that sets it.