Privately made firearm in the US: results from a national survey.

Almost nothing is known about the size or composition of the stock of privately made firearms (PMF). Estimate the size and composition of the U.S. PMF stock. A probability-based online survey of US adults conducted in December 2024 were used to generate nationally representative estimates. 12,907/ 20,907 adults (59%) responded to the survey invitation; 4,059 owned a working firearm. Respondents were asked whether they owned PMFs, defined as "firearms that were NOT produced by a manufacturer (sometimes called privately made firearms), such as guns that were assembled from a kit, 3-D printed or otherwise put together" and if so, how many and what types. They were also asked about their most recent PMF acquisition. We estimate that 2.9 million [CI: 2.2 million, 3.8 million] US adults own approximately 10.1 million PMFs. Most were constructed from kits (34%) or unfinished parts (32%); 16% were 3D printed, and the remainder were machined from raw materials (18%). Half 49% [CI: 0.43, 0.53] were unserialized. Among US adults who last acquired a PMF within 24 months of the survey, 67.2%, [CI: 48.7, 81.6] had a background check for their most recent acquisition, compared with 45.2% [33.9, 56.9] for PMF owners who last acquired a PMF > 24 months prior (P < 0.05). Comparable statistics for serialization were 68.9% [CI: 51.7, 82.1] and 53.8% [42.2, 64.9] (P = 0.14). Approximately half of the 10 million PMFs owned by US adults were not serialized. More recently acquired PMFs are more likely to be serialized.