A team of researchers in Australia has taken a closer look at a problem that is becoming more visible in forensic casework: how to analyse 3D printed firearms when the usual methods no longer work.
Led by scientists at Curtin University, the study focuses on the plastics used in consumer-grade 3D printers. These materials, most commonly PLA, ABS and PETG, have become central to the production of so-called ghost guns, weapons that can be made at home and often lack serial numbers or do not reliably produce traceable toolmarks. What makes them particularly difficult to investigate is not just how they are made, but what they leave behind.
Traditional firearms analysis relies heavily on toolmarks. Examiners look for distinctive impressions on bullets and cartridge cases to link a weapon to its use. With 3D printed guns, those markers are often absent or too inconsistent to be useful. In some cases, including Liberator-style designs cited in prior studies, even basic features such as rifling are not identifiable, leaving little for investigators to work with.
The Curtin team approached the problem from a different angle. Instead of looking at physical markings, they examined the chemical composition of the materials themselves. Using infrared spectroscopy paired with statistical analysis, they studied 67 different filament products available on the Australian market, including both raw material and 3D printed samples.
A Method With Clear Limits
The results show that the technique can clearly separate the main categories of plastics. PLA, ABS and PETG each produce distinct chemical signatures, making it possible to identify the base material used in a 3D printed component with a high degree of confidence.
Where the method begins to fall short is at a finer level of detail. The researchers were unable to distinguish between brands, colours, or whether a sample came from raw filament or a finished 3D printed object. That limitation, they suggest, may reflect how standardised the supply chain has become. Many of the products examined are manufactured in the same regions, and may share common sources of raw material, although this cannot be confirmed.
Even so, the study found useful variation within each material type. Modified filaments, such as flexible PLA or carbon fibre reinforced blends, showed measurable differences tied to the additives used to alter their properties. In some cases, those differences raised further questions.
A flexible PLA sample, for example, showed strong similarities to PETG, which may indicate a blended composition, although this cannot be stated with certainty. Other samples marketed under a single label also appeared to contain additional components, suggesting possible inconsistencies in labelling rather than confirming them.
One of the more practical findings relates to the structure of the filament itself. While the material inside a spool was consistent along its length, the outer surface often told a different story. The researchers found evidence of a coating, likely applied during manufacturing, that produced a separate chemical profile.
That layer was experimentally shown to be reducible using ethanol cleaning, but if left unaccounted for, it could lead to misleading comparisons between samples.
Where You Sample From Matters
3D printed objects, meanwhile, tended to reflect the inner composition of the filament more closely than the outer surface. There were exceptions.
Some 3D printed samples showed mixed chemical signals, which the researchers attribute to residue left in the printer nozzle from previous jobs. In practice, that means where a sample is taken from a 3D printed object could matter, with the study indicating central regions may be more representative than initial printed layers.
The study does not position infrared analysis as a complete solution. Its sensitivity is limited when it comes to distinguishing closely related materials, and the authors point to the need for complementary techniques to build a fuller picture.
But it does offer something that has been largely missing in this area: a way to extract meaningful forensic information from materials that were previously difficult to interpret.
The study lands at a moment when ghost guns are drawing increased regulatory attention across multiple jurisdictions. In the United States, the ATF moved to close serial number loopholes on privately made firearms in 2022, while Australia maintains strict controls on firearm manufacture that make 3D printed weapons illegal regardless of design.
What has lagged behind the policy response is the forensic infrastructure to support it. Investigators have needed tools to analyse weapons that, by design, resist conventional analysis. Chemical profiling of printed materials does not solve that problem entirely, but it adds a layer of investigative capability that did not previously exist in a structured, tested form.
The study is titled “Forensic characterisation of 3D printing polymers used for the manufacture of privately made firearms using ATR-FTIR spectroscopy and chemometrics,” and conducted by Michael V. Adamos, Kari Pitts, Simon W. Lewis, Georgina Sauzier.
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Featured image shows annotated infrared spectra of PLA, ABS, and PETG 3D printing filament. Image via Forensic Chemistry.
