Why Does a Rifle Crack? 



By Edward C. Grossman 



A WAR strength infantry company 

 lay in our rear. We walktsl 

 toward its far-off target, nearly 

 in the line the bullets would take, a 

 few yards' divergence to the left giving 

 us the safety margin w^e felt would be 

 enough with such expert marksmen. 

 From some indefinite point in the air to 

 our right, there came a sudden 

 burst of high, thin, eerie crashes, the 

 thin crash that comes from the leap of 

 the electric spark from the static ma- 

 chine, repeated in fitful fashion. Most 

 extraordinarily, the sound lacked any 

 definite point of origin ; it seemed higher 

 than we were; and it seemed to come 

 from our right. Nearer than this we 

 could not locate it. A slight lull in the 

 sharp crackling, and there came another 

 sound — the heavy, dull thudding of 

 guns fired at a great distance. As we 

 progressed toward the long fire target 

 twelve hundred yards from the infantry, 

 the queer crackling noise followed us, 

 growing thinner and more weird, but the 

 thudding of the far distant guns grew 

 fainter. 



PhotOKraph by Or- 1 nance Dcparlinrnt. V, . S. N. 



The bullet was photographed when six 

 inches from the muzzle, just escaping from 

 the blast gases of the rifle. Note the 

 outline of the sound wave diverging 

 from the nose of the bullet. This is the 

 first stage of the exit of a bullet from a 

 rifle's muzzle. It is not unlike the bow 

 wave of a boat 



Photograph by Ohlnanco Depart 



This picture was taken when the bullet 

 was eight inches from the muzzle, and 

 traveling at a speed of roughly a half-mile 

 a second. The two wires making the 

 contact and the electric flash by which 

 the photographs were made are shown 

 as two black lines. The bullet takes its 

 own picture. Note the eddying effect 

 of the air behind the bullet. The fastest 

 mechanical shutter, giving an exposure 

 of one-thousandth of a second, would 

 allow the bullet to move 2.7 feet during 

 the opening of the lens 



We were walking not more thai,! one 

 hundred or one hundred and fifty yards 

 from the line of fire of a trained infantry 

 company, delivering its fire at a group- 

 target twelve hundred yards, roughly 

 three-quarters of a mile, away. 



The thin, high-pitched crackling, that 

 seemed at one time like the leap of the 

 high-tension spark of the static machine, 

 at antjtlier like the cracking of whips, and 

 again like the vicious crash of a stone 

 through glass, came from the flying 

 bullets of the United States service 

 rifle, which starts with the speed of 

 twenty-seven hundred feet per second. 

 The thudding, that fell oft' to almost 

 nothing at twelve hundred yards, came 

 from the rifles themselves, the only 

 sound one hears when close to them, 

 but the least noticeable at a distance 

 when one is close to the course of the 

 bullet. 



As we gained the target, a new sound 



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