One thing that wasn't mentioned in the article is that he had to embed a metal block into the plastic so that the gun was detectable on an x-ray machine. This was to comply with the Undetectable Firearms Act of 1988.

Could someone who had a printer and the downloaded file skip that part? Yes. But they could possibly be fined and jailed for up to 5 years.

http://www.gpo.gov/fdsys/pkg/STATUTE-102/pdf/STATUTE-102-Pg3...