Dexter Taylor is serving 10 years for doing so in NYC without a license[]. The guns were never used or even left his home, and he is not otherwise involved in crime.

Also in NY it's illegal to make an unserialized firearm. I have no idea what the serialization requirements are there, but what California did was require you report them to DROS.

Also, federally, not legal advice -- but I'm not aware there's any law against selling it. You just can't manufacture it for the purpose of sale or transfer. If it is incidentally sold later it's just like any other firearm without a serial number that's also legal (namely those manufactured commercially before the GCA, or those manufactured non-commercially by private persons after the GCA). I've seen the claim "can't transfer or sell it" over and over on all kind of gun forums etc but no one has ever been able to point where that is blanket illegal.

[] https://en.wikipedia.org/wiki/Dexter_Taylor