Posted on 09/25/2016 10:03:53 AM PDT by w1n1
When a bullet is fired, the rifling of the barrel puts a twist on the bullet in order to improve accuracy, increase the distance traveled, and to stabilize the bullet as it moves through the air towards its target. Twist rates are often set up as a ratio, such as 1:14, 1:12, or 1:7, which refers to inches per turn. A twist rate of 1:10 means the bullet will turn one time in 10 inches of the barrel.
Rifling was discovered in 15th century Germany and most likely took the science behind arrows, which are fletched in a way that the arrow spins, thereby increasing its accuracy. It did not gain popularity until the 18th century, and was a crucial tool for the young United States to beat the British in the Revolutionary War. Nowadays, gunsmiths use either cut rifling or button rifling to produce this effect, but either technique effectively adds raised lands and depreciated grooves along the length of the barrel that cause the bullet to rotate before it ever leaves the gun. Read the rest of the story here.
I assume he means speed of rotation.
And the longer the bullet, the faster the twist rate required to stabilize the bullet.
The twist does effect velocity, but not by much.
http://bulletin.accurateshooter.com/2015/02/does-barrel-twist-rate-affect-muzzle-velocity-litz-test/
https://en.wikipedia.org/wiki/Miller_twist_rule
The twist rate also affects chamber pressure for a bullet of a given mass. There is a limit to the tightness of the twist, after which the bullet merely scrapes off into the groves.
I found this episode of “Mythbusters” fascinating.
“Bullet Fired vs. Bullet Dropped”
https://www.youtube.com/watch?v=abUBrQmI33Q&list=PLOdnh5J_7Iy7KerFi9J_HX0nPLndzo_F7&index=5
“Bullet Fired vs. Bullet Dropped”
It just shows that earth's gravitation pull was constant for the two bullets.
I get that.
But can any level of “rifling” change this ?
I doubt it can change the “Gravity” aspect, but can it change or improve the velocity ?
I mean, we hear about these snipers that take out their targets from a mile away. At what point, over what distance will the bullet lose the velocity required to get the job done?
A bullet dropped from 30,000 feet will reach terminal velocity and may or may not be deadly. A bullet fired from a gun starts out well ahead of terminal velocity but at some point will be reduced to such.
What is that number/distance when the physics take over and make the “fired” round ineffective?
***A bullet dropped from 30,000 feet will reach terminal velocity and may or may not be deadly.***
Years ago I read about small metal darts that were dropped on infantry in WWII. Hardened heads were supposed to be more effective than strafing. Ever so often I would see these darts at a gun show.
I got a call this year from Texas in which a 50 cal FMJ bullet hit a double pained window, broke the outer glass then dropped to the sill. It did not break the inner glass. I figure someone far, far, away fired it. The owner was so glad no one was targeting him!
“There is a limit to the tightness of the twist, after which the bullet merely scrapes off into the groves.”
There’s also a limit whereby the centrifugal force is high enough to tear the bullet apart.
Then, there’s “Gain-Twist”...
I have a copy of Hatcher's Notebook and it is a must have for any firearm library.
Miller's formula is not in it as Don Miller published his formula in 1995.
That is called the "Maximum Effective Range". The range beyond which you may miss your target, thus your round is ineffective.
http://www.appliedballisticsllc.com/Articles/ABDOC101_1_MaxEffectiveRange.pdf
Minimal energy causing round ineffectiveness is another matter entirely.
“A bullet fired into the air can return to earth at speeds between 300 and 700 feet per second, fast enough to pierce a person’s skull,”
http://forensicoutreach.com/library/the-falling-bullet-myths-legends-and-terminal-velocity/
I sure wouldn't want to get hit by a falling bullet.
It gets complicated when you talk about distances. A faster twist will run up pressures, which has an effect on muzzle velocity. In other words if everything else is equal, you can put more powder in a 1 in 12 than a 1 in 7. If the 1 in 12 won’t stabilize a bullet properly, it will yaw, which will kill it’s effective ballistic coefficient, which will cause its downrange velocity to go to hell. You can see the same effect of too slow a twist on a big bore (think elephant) rifle, the bullet will yaw and penetration on an elephant skull will suck, literally cut it in half.
If in doubt my opinion, is to err on the side of faster twist.
There are interesting home made rifling machines "out there". I'm not sure which one to build. I will noodle through it eventually.
If you take the muzzle velocity and multiply it by the free fall time, you can predict how far a bullet won't get. (Assuming a horizontal shot.)
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