Introduction. The investigation of a problem of range finding is quite important, because it is often needed in crime investigation practice. The existing methods are not always effective enough. Theoretical analysis. The actual problem of existing methods is the search of statistically significant marks of gunshot which allow to determine it short range and acceptable reliability. Methods of research. Simulation, experiment, statistic analysis. Experimental procedure. The aim of the research was the analysis of the significance of the size of peripheral zone of smoke-back deposition as a sing of a shot from the Margolin. The size of zones was measured though the experimental evidence got with the use of purpose designed, 3D printed photometer. The data about the size of zones was analyzed by the mathematical statistics method. Discussion of results. There are several main of the analysis. Firstly, the size of the peripheral zone with 95%confidence allows to differentiate following intervals of MCM gunshots: 0–1 cm, 2–14 cm, 15–21 cm, 22–29 cm. Secondly, the size of peripheral zone of smoke-back deposition dependence on gunshot is not straight – the size first enlarge then decrease. However, only 8,5–9,73 cm size of peripheral zone, that points on a 2–14 cm gunshot can be used as a stand-alone mark. 15–21 cm, 22–29 cm distance intervals can be surely differentiated from each other and from 2–14 cm interval. To differentiate 15–21 cm, 22-29 cm and 2– 14 cm intervals from 0–1 cm besides the size of peripheral zone it is necessary to use other marks additionally.