Few countries systematically record and publish detailed information on the types, caliber, and makes of ammunition recovered by law enforcement. This results in a lack of knowledge of the ammunition used in crime, including in the European context. This pilot study examines the utility of ballistic datasets for monitoring illicit ammunition. The ballistic laboratories of four European countries—Denmark, Germany, Sweden, and Switzerland—provided access to non-confidential subsets of their national databases, including the caliber of recovered cartridge cases as well as the year and type of incident in which they were used. The laboratories also shared images of the ammunition headstamp markings, which helped determine each cartridge case’s manufacturer and—when known—year of production. The resulting dataset covers 3130 cartridge cases documented by the participating laboratories between 2015 and the first quarter of 2020. Although limited in scope—the research team did not have access to geocoded data so spatial comparisons were limited to the country level—the dataset helps generate a baseline of the main varieties of ammunition used in crime, by country and crime category, and over time. Most of the ammunition (61 per cent) was recovered in the context of violent types of crime—homicides and assaults—for which pistol ammunition calibers were the most prominent. 610 unique headstamps were recorded, but only a small proportion of these varieties of ammunition accounted for most of the cases. All four country datasets included both foreign-made ammunition as well as cartridges produced domestically. The year of manufacture could be identified for 28 per cent of the cartridges, and at least 27 pieces of ammunition were produced in the same year that the criminal incident took place, which suggests recent diversion from licit holdings. The dataset revealed additional trends such as the criminal use of blank ammunition in all four case studies, as well as the relatively new prevalence of the 7,62 × 39 caliber—which is typically used with AK-pattern rifles—in one country. In addition to shedding new light on the types of ammunition used in crime in the European context, monitoring illicit ammunition across space and over time has the potential to support police investigations with intelligence on criminals’ sources of supply.