Powder Gases Wash Away Steel Guns 



The process is the same as that by 

 which a river cuts away its banks 



By Edward C. Grossman 



WHEN a modern infantry-rifle cart- 

 ridge is fired in a rifle-barrel, the 

 heat generated by the powder gases 

 is measured by some 4000 degrees Fahren- 

 heit. One 

 shot does not 

 mattermuch, 

 two shots in 

 rapid succes- 

 sion raise the 

 temperature 

 of this steel a 

 bit more, 

 three shots 

 are still 

 worse, but. 

 twenty, fired 

 at machine- 

 gun speed, 

 raise an or- 

 dinary bar- 

 rel to a steak- 

 broiling tem- 

 perature. 



The gases 

 pushing be- 

 hind the bul- 

 let and trav- 

 eling at high 

 speed with 

 the pressure 

 of 50,000 

 pounds to 

 the square 

 inch, literally 

 wash away 

 the softened 

 steel just ahead of the chamber as fast as it 

 is heated by the high temperature of dis- 

 charge. The process is known as erosion — 

 a washing away. When a river sets in to 

 cut away its banks, it also erodes. 



Because machine-guns are fired at high 

 speed and are used for a comparatively long 

 series of shots without a pause, their chief 

 foe is this erosion. If machine-guns were 

 fired as the average layman supposes — one 

 continuous blast of bullets while the argu- 

 ment lasts, they would be out of commission 

 in a couple of thousand shots, which means 

 an actual firing life measured by a few 

 minutes. No cooling system ever invented 



These are American machine guns which have been nreu irom 

 2,000 to 3,000 times. Ahead of the chamber, which is the por- 

 tion where the cartridge rests when the gun is loaded, the 

 barrels are washed away on either side until the bore is larger 

 than the neck of the chamber. The result is that the hot 

 gases rush past the bullet, which does not seal the gap, and 

 wash still more steel away, and so on, around the circle 



will keep down the temperature on the in- 

 side of the barrel with such usage. 



Because of this, because of the necessity 

 for re-laying the gun on the mark every 



twenty shots 

 or so, and 

 because of 

 the slight de- 

 lay in insert- 

 ing a new 

 belt or drum 

 or clip of 

 arrmunition, 

 the guns are 

 fired in short 

 bursts, each 

 followed by 

 a pause. The 

 Germans use 

 two guns at 

 detached 

 points, alter- 

 nating their 

 fire to avoid 

 over-heating 

 and to avoid 

 the delays 

 incurred by 

 inserting 

 new clips or 

 belts. 



Even used 

 in this way, 

 machine 

 guns show 

 erosion very 

 quickly. The 

 photograph shows the barrels of types 

 of American machine guns, fired 2,000 and 

 3,000 shots. As the photographs plainly 

 show, ahead of the chamber, which is the 

 portion where the cartridge rests when the 

 gun is loaded, the barrels are washed away 

 on either side until the bore is larger than 

 the neck of the chamber. 



The result is that the hot gases rush past 

 the bullet which does not seal the gap, and 

 wash still more steel away, and so on, 

 around the vicious circle of damage. The 

 barrels shown in the photographs are 

 sectioned lengthwise, showing only one half 

 of the bore of the guns. 



754 



