Analysis of the Dynamic Behaviour of the Barrel During a Gunshot Using Modal Analysis

In this study, the dynamic behaviour of a .223 Remington rifle barrel was investigated during live firing. A three-dimensional finite element modal analysis was performed and combined with experimental displacement measurements. The numerical model was used to determine and physically classify the first ten eigenmodes of the barrel–muzzle-device assembly according to their mode shapes and dominant deformation directions. The analyses revealed characteristic modal frequency regions at approximately 44.7 Hz, 259.8 Hz, 705–706 Hz, 1349–1356 Hz, and 2153 Hz. During the firing tests, experimental displacement time histories were measured at two locations along the barrel. The Fast Fourier Transform (FFT) was used to convert the time-domain signals into frequency-domain spectra. Experimental spectral peaks were identified independently of the numerical predictions using a local spectral-contrast criterion and subsequently compared with the modal frequency regions predicted by the finite element method (FEM). The most consistently identified experimental frequency components occurred near 270 Hz in the Front displacement spectra, with relative deviations of 3.72–5.30% from the FEM-predicted bending frequency of 259.81 Hz. In the higher-frequency regions, the correspondence between the experimental peaks and the numerical predictions was less consistent across the firing configurations and measurement points. The results demonstrate partial frequency correspondence between the experimentally measured barrel response and the numerical modal predictions. However, the presence of spectral peaks at comparable frequencies alone does not confirm the experimental identification of the corresponding mode shapes. The findings therefore highlight the importance of distinguishing between frequency correspondence and the independent experimental identification of individual vibration modes.