Introduction. In practice there are cases of the crime investigations involving firearms which deal with criminal’s usage of cartridges, not intended for this weapon. As a rule, that happens because of the lack of the regular cartridges. Criminals use some tricks to adapt them for the shooting of a particular weapon models to use them. Experimental part. The article presents the results of experimental studies in the footsteps of bullets and cartridge cases on contingency cartridges with their pistol shooting of «Mauser K 96» of 1896, caliber of 7,63 mm and pistol «Browning» of 1900, caliber of 7,65 mm. Revealed traces compare with traces of bullets and cartridge cases on regular rounds. The specific traces of firearms on shot bullets and spent cartridges indicating the use of non-standard cartridges are defined. Discussion of results. Possibility of using the results of the work during the inspection of the scene and forensic ballistic examinations is revealed. Conclusions. Marks on bullets and cartridge cases for defining the model used weapons are defined. The possibility of identification of firearms and bullets shot by spent cartridges using contingency cartridges is solved.