FACTS ABOUT THE LIFE OF GUNS.

Oamaru Mail, Volume XLIX, Issue 13909, 10 November 1919, Page 7

FACTS ABOUT THE LIFE OF GUNS.

The life of a pun depends upon the progress of erosion, which sooner or later is certain to impair the accuracy of the fire. Erosion is caused by the action of the explosive erases at high temperature and pressure. The hot gases cause a thin film of steel to absorb heat. The film expands and becomes set. Upon the i-elease of the pressure it contracts, which action causes minute cracks that grow larger with every discharge. As they increase in size they form passageways for more hot gas, and that tends to enlarge them still further. The inner surface thus becomes roughened and the bands begin to corrode. Finally the bore becomes so enlarged that it allows the gases to escape. The shell does not then acquire its proper rotation, and its rligTit becomes'" erratic. All guns except, small ones are now constructed with linings in the tube, which, when the bore is worn out, are removed and replaced by new ones. The cost of relining a. gun is approximately 30 per cent, of the cost of the gun. There appears to be no limit to the number of times that a gun can be relined. The small arms used by the United States Army are considered to be worn out after 5,000 to 7,500 rounds have been fired. Small naval guns can be fired about 1,000 times before they are regarded as worn out. Large twelve inch and fourteen inch naval guns are considered to have a life, on one lining, of from 150 to 200 rounds. Low velocity guns, such as howitzers and mortars, have correspondingly longer lives than high velocity guns of the same calibre, because of the pressures they develop, and hence the the lower temperatures.