Topic: 3d Printed Weapons
Keywords: "3d Printing" "three -dimensional printing" (be prepared for variant spelling, they might give your searches different results) "guns" "Defense Distributed" "military technology"
Using Academic Search Premier the best results were achieved search "three-dimensional printing" AND "Weapons" as two separate terms. The results were 10 articles. 4 were scholarly and 3 of those were full text access.
The Library catalog only offers one relevant book for 3d printing, Fabricated: the New World of 3D Printing. The other 4 books that resulted from that search matched the keyword for being the 3rd edition published.
Better luck was had in the eBook collections. Ebsco eBooks gave 10 books for a "3d printing" search. eBrary gave a surprising 11882 for "3d printing."
Academic Search Premier and Ebsco eBooks have built in citation tools that allow you to send an email to yourself along with either full text pdf/html or a stable link for access. eBrary (through Proquest) also has similar features. Not all databases have these tools, but when they do take advantage of them!