There are a number of companies producing unfinished lower receivers that are then sold to consumers to complete the machining on. Lowers that are only 80% complete are not classified as “firearms” and thus require no FFL transfer. While a CNC machine is ideal, the kits can be completed using tools as rudimentary as a drill press or a router. Polymer lowers are also available and can be completed using a something as simple as a dremel tool. 80% Glock lowers are also available and are quite popular. Firearms made in this way are perfectly legal though they cannot be sold or transferred as they have no serial number.