Gun Tube/Charge/Projectile Interactions and Gun Tube Wear

During initial testing of the first US stick propellant charge for howitzer applications, the M203A1, an unusual asymmetric wear pattern developed. Virtually all wear which occurred during the 3000 round test was located in the top quadrant (10-2 o'clock) of the tube near the origin of rifling. Further complicating the analysis was the use of a 'simulator projectile', the PXR6325, in lieu of the fielded M549A1 projectile for the wear study. This study was initiated to determine if the PXR6325 projectile had unduly influenced the wear results and to determine how stick propellants differ from their granular counterparts in the processes producing gun tube wear. These questions were addressed in a three-pronged attack in which: a) historical US and NATO stick propellant wear data were analyzed; b) the two projectiles under study were compared using physical properties and finite element modeling; c) a matrix of test firings in a highly instrumented gun tube was conducted to measure properties such as heat transfer and gun tube strain at various circumferentially separated points of interest. As a result of these efforts, the contributions of the stick charges and different projectile designs on asymmetric gun wear were discerned. Using these data, the results of a subsequent stick charge wear retest using a new gun tube and a different projectile were accurately predicted. Keywords: Howitzer gun tube wear; Propelling charges; 155-mm Howitzers; Asymmetric wear; Thermocouple data; M203A1 Propelling charge.