Projectile Driving Band Interactions With Gun Barrels

This paper discusses results from a series of trials carried out to determine the effect of the projectile driving band on the stress applied to a 155 mm gun barrel during firing. The interference between the driving band and gun barrel can apply significant loads to the barrel and, in extreme cases, lead to premature cracking and failure of the barrel. Strain gage data from firing trials has been used to characterize the external strain from firing different projectiles and charges to identify potential problems and provide information for fatigue analysis. Very high band strains were routinely measured under "oiled bore" conditions, i.e., after barrel cleaning and also during the first one to three rounds of a serial following a long pause in firing, such as at the start of a day's firing. In general, the strain associated with the driving band was seen to decrease with increased charge zone, barrel wear, and, at higher charge zones, distance along the barrel. In the majority of tests fired at maximum charge, there was no strain peak associated with the driving band in the forward part of the barrel. In conjunction with these experimental observations, a laboratory study has been carried out on the effect of a narrow pressure band on the deformation of a thick-walled tube. An apparatus was constructed in order to pressurize a known length of a smooth-bore cylinder. Sealing width at the edges of the band was minimized to reduce edge effects, and an oversize pressurized "cap" was used to ensure that the bandwidth remained constant during the experiments. Spacer disks were used to vary the bandwidth and also to adjust the cylinder position relative to the band. Measured external strains on the tubes were compared to calculations based on analytical solutions for step pressure changes and are shown to be in good agreement.