A mixed composition particle highlights the formation mechanism of the weapon memory effect phenomenon

•Formation mechanism of mixed composition particles.•X-ray mapping of mixed composition particles.•Memory effect observed using different ammunition in the same weapon.•Mixed composition particle having a domains structure. A shooting event involved several types of ammunition that were all shot from a single firearm. GSR analysis of samples taken from the suspect’s hands, hair and from his clothes was carried out. Mixed compositions particles were found among other GSR particles, attributed to the weapon memory effect. SEM/EDX analysis of these particles highlighted a particle with defined domains containing distinct groups of elements. Some of these elements were absent in the primers mixtures of the ammunition used in the shooting event. X-ray mapping indicated that these domains might have been incorporated into the particle within several shooting cycles. This combination of compositions created an opportunity to shed light on the formation mechanism of “memory effect” particles. The aim of the study is to highlight such particles way of formation.