New York mandated gun-file detection. A padding tool arrived to change every hash.

Hash matching is the cheapest way to satisfy a statute that asks for detection software. It needs no understanding of what a part does, only a list of known-bad file fingerprints and a comparison against it. It is also the method that a handful of appended bytes defeats, which is what Cody Wilson says his tool does: pad the file, change the hash, leave the printed object working as intended ^[6]. The Verge is careful to describe hash-keyed identification as how such a system would work in theory ^[5], so nobody has confirmed that is what New York's mandated software will do. The incentive is the problem. A law that names a capability and says nothing about a failure rate gets the implementation that is quickest to ship.

Then the arithmetic. Wilson says DEFCAD holds more than 200,000 files of gun designs and components ^[4]. A vendor building a blocklist against that catalogue starts at 200,000 entries, and Wilson's stated design changes the hash of every file as it is created and downloaded ^[7], so the size of the list stops tracking the number of designs and starts tracking the number of downloads ^[2]. He says he has begun applying the treatment across DEFCAD by default and intends to release the tool as open source, which would let any individual scramble a file they already hold ^[8]. He calls this self-defense against New York "trying to reach into the internet and police how open-source 3D printing is done" ^[3]. A printer that ships with a list compiled at manufacture remains compliant with the statute for its entire service life while matching a smaller and smaller share of what is actually in circulation.

The seizure numbers explain why the mandate exists and also why it is a poor fit. The NYPD confiscated one 3D-printed gun in 2021 and 109 in 2024 ^[10], a 109-fold rise across three years ^[1], and Everytown reported similar upticks in 20 other cities ^[11]. Set against conventional firearms confiscated nationally the printed share is still comparatively small ^[12], in a country where guns are estimated to outnumber people ^[13]. Capability has moved further than volume: Wilson's 2013 Liberator fired a single shot ^[14], while designs like the FGC-9 fire multiple high-velocity rounds without breaking and have turned up with neo-Nazi cells in Europe and rebel groups fighting Myanmar's junta ^[15]. The Verge argues the components are arguably more dangerous than the guns, since switches and suppressors are otherwise illegal or licensed and printing routes around that ^[16].

Luigi Mangione, who admitted to shooting and killing UnitedHealthcare CEO Brian Thompson and is awaiting sentencing, allegedly used a partially 3D-printed pistol ^[17]. Whatever stands between a file like that and a printer, it is not a check that a few junk bytes at the end of a file will pass.