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Does rotation of bullet when fired increases its lethal power?

  1. Feb 16, 2013 #1

    I was watching Discovery channel the other day and it was showing a series on evolution of guns and ammo..
    It showed that earlier there was bolt mechanism for firing the gun. And then, a revolution came when muzzzle or bullet was shot such that it went in forward direction while rotating.

    This makes me wonder. Does rotation really increases lethal power of a firearm? and what is the principle behind this?

    Thanks in advance
  2. jcsd
  3. Feb 16, 2013 #2


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    I'm not clear on what you mean by a 'bolt mechanism' for firing a gun.

    However, in the early days of firearms up to the mid 19th century, the projectile was a round ball, usually loaded after the gunpowder had been put in the gun. When the gun was fired, the spherical shape of the projectile was naturally stable in flight.

    When separate loading gave way to cartridge ammunition, the shape of the projectile changed to a shape which was roughly cylindrical with a conical end. When such a projectile is fired through a gun barrel with no rifling, after leaving the gun, the projectile will tumble due to its shape and the uneven aerodynamic forces it experiences.

    It was found that if a gun barrel is rifled so that the projectile is spinning about its axis of flight, then the inertial forces caused by the spinning overcome the instability caused by the aerodynamic forces tending to cause the projectile to tumble. If the projectile cannot tumble, its range tends to be greater.
  4. Feb 16, 2013 #3
    "Bolt action" describes a hand-operated moveable mechanism that locks a metallic cartridge in place in the "firing chamber" of a typical rifle. A pointed cylindrical bullet fired from such a rifle with spiral rifling in the barrel will spin, thereby contributing to stable, straight flight of the bullet. The velocity of a spinning bullet is maintained longer, thus retaining its striking and penetration power.
  5. Feb 16, 2013 #4
    OK. Got it. thanks for your help!!
  6. Feb 16, 2013 #5
    The rotation of the bullet helps it remain stable in fight. Expending energy into the rotational mode of the projectile will result in a slight loss of linear kinetic energy. So yes the "power" of the shell will be slightly diminished.
  7. Feb 18, 2013 #6
    Bolt action has nothing to do with the rotation, it is merely a way to feed ammo and strongly seal the breech against the 50,000 psi (average, modern rifles) operating pressure. Other actions include lever, pump, gas-operated, recoil operated etcetera ad infinitum.

    The reason the bullet is made to spin is for accuracy. The first rifles (as opposed to muskets, which were smoothbore like a shotgun) were muzzle-loading and used round balls. This means the powder was poured into the barrel and a round lead ball was rammed down the barrel with a ramrod. At the time, a well trained soldier could fire 5 shots a minute with a musket, using a rifle reduced it to about 3 shots a minute as it was harder to ram the ball down the tighter, rifled barrel. The great advantage was that a musket was accurate on a man-sized target at perhaps 50 yards, a rifle out to about 200 yards, this kept increasing until, at the time of the US Civil war, shots were being made out to 400 yards with rifles while muskets were still only accurate at about 50 yards. This is why you see in movies about old wars great masses of men standing in formations all firing at once, just chance would make a whole formation accurate because of huge volleys of fire.

    As to your question regarding increase of lethal power, the other poster (s) were correct that it increases accuracy and therefore lethality, and that spinning the bullet uses some of the power that would otherwise add to speed.

    As to your real question, I believe it does increase lethality, and here's why: Bullets don't just spin a little bit. A hypothetical bullet with a 1:12 twist (one revolution every 12 inches) traveling at 3000 feet per second (FPS) would be spinning at 3000 revolutions per second, or 180,000 revolutions per minute. This is actually very close to an M16 (AR15) round from a 20 inch barrel.

    I believe this contributes to the fragmentation of the bullet within the target, and therefore, greatly to the lethality. I know the energy of rotation is dumped into the target and therefore must contribute to lethality.

    This is more pronounced in the higher speed projectiles of rifles, but pistol (also rifled for accuracy) bullets are also affected, I believe the rotation helps fragment the bullet and particularly opens hollow points faster than a non-rotating bullet would.
  8. Feb 18, 2013 #7
    For guns with same muzzle energy ( as the stats show it), there is a considerable difference in the lethal power.... Is this due to the same effect?? A rifle and a pistol for example...
  9. Feb 19, 2013 #8
    In the most basic sense, the gas has more time to expand in a longer barrel thereby increasing the time accelerated of the projectile. Of course, the rate of acceleration decreases as the distance the bullet travels inside the barrel expands.
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