Study on the Vibration Response of an Automatic Rifle Barrel in Hot and Cold States

To gain a deeper understanding of the vibration characteristics of an automatic rifle barrel in both hot and cold states, a non-contact measurement method was used to measure the amplitude and vibration velocity of the barrel during single and repeated shots of a small-caliber automatic rifle. Displacement and velocity curves of the barrel vibration were obtained, and the muzzle vibration in hot and cold states was compared. The study also analyzed the effects of firing loads and the elastic modulus of the barrel material on the barrel’s vibration in a hot state, as well as the applicability of the eccentric rotating stepped beam model. The formation mechanism of the differences in vibration response between hot and cold states was revealed. The research results show that: (1) In both hot and cold states, the muzzle vibration pattern begins with a downward movement of the muzzle, followed by a significant upward motion. After three cycles of forced vibration as the bullet exits the muzzle, the barrel enters a free-damping vibration state until the vibrations dissipate. During Repeated shots, the barrel vibration accumulates, resulting in a larger amplitude than single-shot firing. (2) In the hot state, the barrel’s amplitude and velocity increase, while the vibration frequency decreases. The main reasons for the increased amplitude in the hot state are the decrease in the elastic modulus of the barrel and the increased firing load. (3) The eccentric rotating stepped beam model applies to calculating muzzle vibration in the hot state.