Abstract: The life firing experiment was carried out to investigate the damage evolution law of 12.7 mm large caliber machine gun barrel and its influence on elliptic hole. Optical microscope, scanning electron microscope, endoscope and caliber gauge were used to observe and measure the damaged barrel, and the damage rule of barrel bore during its life cycle was obtained. The results show that three typical barrel damage regions of 12.7 mm machine gun are at the initial position of refiled bore, the high bore pressure zone and the muzzle of barrel. The damage rates and modes are different in these three regions. The Cr layer in the initial region of refiled bore has a high shedding rate, leading to a high expansion rate of the inner diameter. In the early stage of the high bore pressure zone, the Cr layer remains intact, but in the later stage of life, the Cr layer falls off faster. The Cr layer at the muzzle of barrel is almost not shed, and the damage is mainly caused by wear. The barrel life of machine gun ends in the way of keyhole of bullet exceeding the standard. The forming reason of keyhole of bullet is that the refiling lands are damaged and stripped, which weakens the driving ability of refiling and makes the warhead rotate at a low speed, thus leading to the keyholes of bullet.

Key words: barreldamage, Crlayer, rifling, keyholeofbullet, endoflife