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Appendum to Ballistics 101


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When all firearms are discharged, their barrels vibrate in the same manner as the tine of a tuning fork. These vibrations will cause the barrel to move conciderably and with violence. Accuracy is absolutely dependent upon the uniformity of these vibrations and a fundemental requirement of a good gunsmith is the ability to forge and work steel in such a manner as to maximise the barrel's capability of ringing true with each and every shot. Barrel vibrations are divided into two parts: One, "Fundamental" and Two, "Secondary" vibrations. With fundamental vibration the entire barrel vibrates as a single unit from one fixed node (the point at which the barrel is calm) which is at the breech where the barrel is fixed to the reciever. Secondary vibration is a series of overtones in which the barrel is divided longitudinally into a number of vibrating sections each terminating in a node at the end of a particular section nearest the breech. Some of the things which if not done just right, which will adversely effect the true ring of a barrel are headspace, screws, crowning, throat, bore and bedding. Bedding screws that are not perfectly true, improper bedding, and bolt lugs and barrel bands that are not uniform, and note this Mr. Marsh: *SET-SCREWS IN THE RECIEVER-RING WHICH APPLY A POINT OF FORCE AT A SINGLE NODE ON THE BARREL-BREECH* can and will cause conflicting stresses when the rifle is fired, altering the barrel vibrations to the point of irregularity, thus destroying any hope of uniform downrange accuracy. [Note:] Many of these enumerated defects are known to be present in WWII M38 Carcanos. Fundamental vibration is set in motion by the shock of discharge. The breech end of the barrel when it is properly melded to the reciever, remains relatively calm and is the single node. The muzzle oscillates in a circular path and can move in any direction through 360 degrees. The position of the muzzle at the instant of bullet exit greatly influences the point of impact on the target. When fundamental vibration is extream and when the muzzle position (at the instant of bullet exit) varies from shot to shot, all hope of down range accuracy is lost. Secondary vibration occures at the same instant as, but independently of, fundamental vibration. In it are a series of nodes and overtones traveling along the length of the barrel producing oscillations similar to that of a snapping whip. Any factor, such as the condition of the firearm, heat of the barrel, powder charge variation, support of the firearm, etc., which introduce small variations in vibration will effect down range accuracy. Almost every aspect of a rifle-cartridge combination will have some effect on barrel vibration. A heavy load will set up a more violent vibration than a light load. On the other hand, when the velocity is low, (such as the light loaded Carcano) vibrations have more time to develop before the bullet leaves the muzzle. Now note this Mr. Burke: * THE TOTAL DISTURBANCE FROM A LIGHT LOAD, THOUGH LESS VIOLENT AND RAPID, WILL BE GREATER THAN THAT OF A HEAVY LOAD.* A properly sized bullet fits the barrel and forms a nearly perfect gas seal. thus expanding gas is trapped is trapped behind the bullet and is pushing equally in all directions. The force of the gas actually expands the barrel behind the bullet. Note again Mr. Burke: *ANY CHANGE IN THIS FORCE NOT ONLY CREATES A CHANGE IN MUZZLE VELOCITY DUE TO A CHANGE IN FRICTION, BUT ALSO CHANGES THE BARREL STRESSES WHICH EFFECTS VIBRATION. To give the readers a sense of the real-world impact of barrel vibration on a bullet's terminal ballistic point of impact: Tests conducted by the US Army on the venerable old M1903 Springfield Rifle which is superior to any M38 Carcano by several orders of magnitude, using standard military ammunition, the angular movement of the muzzle due to vibration equal to more than 40 ft. at 1,000 yards. This is the reason why the M38 Carcano is generally concidered a piece of crap to members of my trade.

With Regard,

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"It is not the critic who counts, not the one who points out

how the strong man stumbled or how the doer of deeds might

have done them better. The credit belongs to the man who is

actually in the arena, whose face is marred with sweat and

dust and blood; who strives valiantly; who errs and comes

short again and again; who knows the great enthusiasms, the

great devotions, and spends himself in a worthy cause; who,

if he wins, knows the triumph of high achievement; and who,

if he fails, at least fails while daring greatly, so that

his place shall never be with those cold and timid souls who

know neither victory nor defeat."

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