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Malik1
22-11-2009, 07:10 PM
What is rifling twist and what does it do?

The rate of rifling twist determines the optimum bullet weight for a given caliber and speed of the bullet by applying the proper spin on the bullet to prevent the bullet form yawing and pitching.

Expressed in terms of the number of revolutions per inch of barrel length, this ratio is commonly expressed by designations such as 1:10, 1/10 or 1 in 10 twist, the 1 represents 1 twist, the 10 represents inches of barrel length.

So, a 1 in 10 twist is, 1 complete bullet revolution every 10 inches of barrel length traveled.

How do you know what rifling twist is right.

A good rule of thumb is that the heavier and longer a bullet is, the faster the rifling twist rate needs to be to stabilize it in flight, therefore a lighter shorter bullet needs a slower rifling twist rate to give proper bullet spin for correct flight.

Exception to the rule.

If an insufficient twist rate is used, the bullet will begin to yaw and then tumble; this is usually seen as "keyholing", where bullets leave elongated holes in the target as they strike at an angle.

Once the bullet starts to yaw, any hope of accuracy is lost, as the bullet will begin to veer off in random directions.

A too-high rate of twist can also cause problems. The excessive twist can cause accelerated barrel wear, and in high velocity bullets an excessive twist can cause bullets to literally tear themselves apart under the centrifugal force.

Choosing the right rifle.

When choosing a rifle cartridge you should always evaluate what you are going to use the rifle for and then select the rifle with the correct rifling twist rate for your imparticular use by bullet weight to gain the most accuracy.

Pitching. Suppose that a bullet is travelling in a straight line. If due to some reason (I don't want to discuss the reasons else it becomes a physics class) its nose goes up or down it is called pitching. A pitch motion in an aircraft is an up or down movement of the nose of the aircraft.

Yaw. Suppose that a bullet is travelling in a straight line. If due to some reason (I don't want to discuss the reasons else it becomes a physics class) it nose goes left or right it is called yawing. A yaw motion in an aircraft is a movement of the nose of the aircraft from side to side.

MUSTANIR
22-11-2009, 11:45 PM
very informative sir can we determine the accuracy of a rifle by barrel length only and does it differ with different calibres

Malik1
23-11-2009, 12:29 PM
Bro in my opinion, accuracy is a combination of type of barrel, type of ammo used, type of sighting system, appropriate number of twists in the rifling for the weight of bullet being used and so on. While the purpose of barrel is to give direction and required energy to the bullet / projectile and in case of rifles, to impart spin stability to the projectile / bullet. The length of barrel controls the duration for which a projectile or bullet is exposed to the pressure of gases produced (due to burning of charge). Longer the barrel more presure a bullet is subjected to, more pressure it is subjected to more muzzel velocity it will have and more muzzle velocity it has flatter the trajectory it will have. If the trajectory is flatter even if you are wrong in range estimation you will still be able to hit the target, so if this is what you call accuracy, I tend to agree with the statement, else in my humble opinion length of barrel does not have to do some thing with accuracy.

Please also remember that there has to be a very fine balance drawn or what they call a happy blend of muzzle velocity, wear and tear of barrel of barrel, recoil, weight of barrel, material to be used for bullets, effects desired at target end, economy etc etc. You simply can not subject a bullet to enormous pressures to make it shoot flatter or simply can not keep extending the barrel to achieve more MV. If a bullet is subjected to more pressures than it is designed for to sustain it tends to shatter due to centrfugal forces and excessive wear and tear, apart from either damaging or reducing the life of barrel.

There is another statement in ballistics which I qouted earlier as well in some thread and it says that once the projectlie leaves the muzzel, if the pressure behind the projectile is equal to atmospheric pressure the projectile will achieve very long range, but for this you need a barrel many hundereds of meters long which is practically not possible.

I hope I have been able to answer your question in my humble capacity.

Glocky
24-11-2009, 12:24 AM
Thanks for the informative post, made good reading.