I believe these events/places where folks were pressing a button to go from billet to receiver were shut down by BATFE some years ago (see ATF Ruling 2015-1 - https://www.atf.gov/media/19161/download)

> An FFL or unlicensed machine shop may also desire to make available its machinery (e.g., a computer numeric control or "CNC" machine), tools, or equipment to individuals who bring in raw materials, blanks, unfinished frames or receivers and/or other firearm parts for the purpose of creating operable firearms. Under the instruction or supervision of the FFL or unlicensed machine shop, the customers would initiate and/or manipulate the machinery, tools, or equipment to complete the frame or receiver, or entire weapon. The FFL or unlicensed machine shop would typically charge a fee for such activity, or receive some other form of compensation or benefit. This activity may occur either at a fixed premises, such as a machine shop, or a temporary location, such as a gun show or event.

> A business (including an association or society) may not avoid the manufacturing license, marking, and recordkeeping requirements under the GCA simply by allowing individuals to initiate or manipulate a CNC machine, or to use machinery, tools, or equipment under its dominion or control to perform manufacturing processes on blanks, unfinished frames or receivers, or incomplete weapons. In these cases, the business controls access to, and use of, its machinery, tools, and equipment. Following manufacture, the business "distributes" a firearm when it returns or otherwise disposes a finished frame or receiver, or complete weapon to its customer. Such individuals or entities are, therefore, "engaged in the business" of manufacturing firearms even though unlicensed individuals may have assisted them in the manufacturing process.