Objective      To investigate the features of back wounds and mechanical mechanism of experimental pigs protected by composite armour hit by high speed microstomia Rifle bullet.        Methods      A total of 17 pigs were randomly divided into experimental group (n=9)

control group (n=5) and pressure testing group (n=3). Pigs of the experimental group adopt composite armour (ceramic bulletproof plates +ultra-high molecular weight polyethylene) to protect their back and get shoot by high speed microstomia Rifle bullets aim at T8 back centrum vertebrae. Control group received same procedures as experimental group except shooting equivalence cartridge without bullet. Pressure test group was used to measure local timely pressure shooting by Rifle bullet. The pigs were observed for heart rate (HR)

systolic arterial pressure (SAP)

and electrocardiography and electroencephalography were performed. In 6 h after shooting

the pigs of the experiment and control groups were sacrificed for pathological observation.       Results      Composite armour was not broken in the experimental and pressure test groups. Local muscle tissue received obviously increased pressure at the shooting time. No obvious change was found in HR

SAP

and electrocardiogram between the experimental and control groups. Significant blunt injury was seen in the spinal cord covered by armour. Mild bleeding was found in the endocardium

lung

liver

kidneys

and spleen.       Conclusion      When high speed microstomia Rifle bullet shoots pig back with composite armour

the spinal cord

cavitas thoracis

and peritoneal cavity tissues have blunt injuries with different severities though the armour was not disrupted. This may be due to back passive state impact caused by the armour distorted quickly and increase of local pressure.