Introduction. This article deals with some issues of forensic investigation of civilian firearms manufactured based on combat samples: features of trace formation on bullets and cartridge case design changes of the original models (samples) of the firearms. The authors highlight the problem of the lack of a literary base and illustrative material, necessary for carrying out diagnostic research of traces on bullets and cartridge cases formed when fired from civilian firearms manufactured on the basis of samples of military weapons. Theoretical analysis. The paper analyzes data of weapons factories, as well as weapons they produce. The authors focus on the necessary terms and examples of the weapon, the design of which was modified and is different from the sample combat weapons. The paper looks at the main provisions of some normative and legal acts of the Russian Federation. Results. The authors identified the groups of traces, formed after firing redesigned weapons, and the place of the location on the surface of bullets and casings.