This paper presents a case study of an incremental design process of a kinetic energy (KE) projectile in which simplifying assumptions that were valid for the initial projectile design were found to be inappropriate for a subsequent projectile design, resulting in a flawed design and led to a material failure. After failure of the projectile was observed, a root-cause analysis was conducted and indicated that column buckling was responsible. This was later confirmed by ensuing analyses. After the flawed assumption was eliminated, a modification to the existing projectiles was analyzed and successfully implemented. The projectile was then redesigned to incorporate the features and lessons identified through this process.