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!
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/
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.
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.)
“get the job done” velocity usually means the bullet has enough speed to both penetrate and expand when it hits the intended target
There are too many variables to give a simple answer to your question.
Here is a fairly in depth discussion of the commonly used .308.
http://www.ballisticstudies.com/Knowledgebase/.308+Winchester+7.62+NATO.html