Three animal models were evaluated in this study involving head impacts of the rat, including the Marmarou drop-weight and two momentum-exchange techniques. In series 1, 36 Wistar rats were hit on the side of the free-moving head using Marmarou’s 450 g impact mass at 4.4, 5.4, and 6.3 m/s. Head acceleration was measured and injuries were observed. The 6.3-m/s side impact resulted in no deaths, no skull fractures, infrequent contusions, and some injuries consistent with diffuse axonal injury. In series 2, 57 Marmarou drop-weight tests were conducted to study head biomechanical responses. Marmarou’s technique involves a head impact followed by prolonged loading into a foam pad under the animal. Based on the literature, the 2 m (6.3 m/s) Marmarou drop causes death, skull fracture, brain and spinal cord contusions, and diffuse axonal injury. These injuries are more severe than that occurring with impact of similar mass and velocity to the free-moving head. Impacts to the free-moving head provide more realistic animal models to study concussion and severe brain injury.