To study penetrating traumatic brain injury biomechanics, a full metal jacket 9-mm handgun projectile was discharged into a transparent brain simulant (Sylgard gel). five pressure transducers were placed at the entry (two), exit (two), and center (one) of the simulant. High-speed digital video photography at 20,000 frames per second (fps) was used to capture the temporal cavity pulsation. Pressure histories and high-speed video images were synchronized with a common trigger. Pressure data were sampled at 308 kHz. The 9-mm projectile had an entry velocity of 378 m/s and exit velocity of 259 m/s. Kinetic energy lost during penetration was 283.7 J. The projectile created temporary cavity with maximum diameter of 54 mm. Collapsing of the temporary cavity drew the brain simulant toward the center of the cavity and created negative pressures of approximately -0.5 atmospheric pressure in the surrounding region. Pressures reached approximately +2 atmospheric pressure when temporary cavity collapsed. A three-dimensional finite element model was developed and validated with the pressure data from the experiment. The model revealed that shear deformations were pronounced in the region immediately adjacent to the projectile path (within 10 mm). Radial deformations extended further away from projectile path and widely spread through the model. These quantified data may assist in understanding injury biomechanics and management of penetration brain trauma.