In this study, transverse and longitudinal accelerations of a full caliber-shell shot by a medium-caliber gun were measured directly during the internal ballistic (IB) phase. The data were transmitted outside the tube by modulation of LASER light emission and recoded into acceleration values. The results were analyzed through the numerical simulation of the response of the tube traversed by the projectile and with the internal-ballistic data providing the longitudinal projectile acceleration. The analysis reveals that the in-bore projectile movements are both influenced by the tube geometry (curvature and straightness defects) and by the tube response during the internal ballistic phase. However, in this work, the tube response appeared to be of greater influence on the projectile dynamics than the tube initial static geometry. Results provide basis for further calibration studies.