Bullet Rise Due to Rifling

[Killermonkey21]

OK. First off, I KNOW that a bullet does not RISE in its path to its target.
I KNOW (thanks to my fiances father who CREATED Modern Ballistics/, a ballistics calculator program) that people may THINK it rises due to the sight angle and bore angle being different. IE you aim straight (level) but your barrel is pointed slightly upward.

What I need is PROOF to show three other individuals from my unit who seem to believe that because of the bullets shape (spitzer) that it generates lift and makes the bullet rise then fall due in its path.

I read a quote from Modern External Ballistics (book) about this, but am not able to find a source online.

Does anyone know where I can prove the laws of physics to these guys online? One of them, an E6, basically told me to put up or shut up. So, yeah.

Any help is appreciated.
-John

 

[expvideo]

The barrel is straight, and so is the flight path. The optic or iron sights are pointed ever so slightly at an angle so that when you are looking through the optic, you are tilting the gun slightly up. that is why the bullet arcs. If the scope was 100% parallel with the barrel, the bullet would simply lose altitude.

It has nothing to do with the rifling or the bullet's aerodynamics creating lift.

 

[D94R]

Are they themselves offering any ballistic data that shows that a spinning bullet creates lift? If not, then you have nothing to prove.

 

[geronimo509]

if he's an E6 and your under that I would not argue with him. You know your right and Expvideo has it right.

 

[amflyer]

Since a bullet is ballistically concentric along the long axis of which it rotates, it's impossible to create lift. Lift is due to a difference in pressure due to airflow over differently shaped portions of the wing. This is why there is a stall speed in an aircraft.

Picture might help:

 

[Funderb]

a sptizer shape can't create lift, see above diagram as to why.

 

[Ithaca37]

Since a bullet is ballistically concentric along the long axis of which it rotates, it's impossible to create lift. Lift is due to a difference in pressure due to airflow over differently shaped portions of the wing. This is why there is a stall speed in an aircraft.

Picture might help:

The above is not really correct

Lift is created due to circulation. The pressure difference is part of the lift generated, but more significant is the redirection of air flow downward. This results in an upward force thanks to conservation of momentum.
http://www.onemetre.net/Design/Downwash/Circul/Circul.htm

The circulation theory is a better explanation because the equal time theory (the one cited by amflyer) require that air flowing over the top of the airfoil reach the end of the foil at the same time as the air flowing under the bottom. The laws of physics do not require this. So while partially true, the theory is insufficient to fully describe lift.

Basically, the bullet's axis of rotation is parallel to path of flight and therefore does not create lift.

 

[heron]

Set up a demonstration, since paper explanations likely won't be believed.

Take a rifle with scope and put it on a good solid rifle rest. Carefully measure the distance between bore center and the scope's line of sight (offset). Make two aiming marks on a target, exactly this distance apart.

At close range (maybe as little as ten yards) use a laser bore sighter to locate the lower point on the target, then hold that position and adjust the scope to zero on the upper point. The line of sight should now be exactly parallel to the bore. Proceed to fire test shots, moving the target further away with each shot, with the scope zero on the upper mark each time. The bullets will hit lower each time you move the target further out. Measure the results and plot the curve.

 

[Mello]

Since the bullet is rotating around its long axis, there is no "up" side which could create lift.

The perceived rise and fall are due to two things. The rise above the sight line is caused by the bullet being launched at an angle above the tangent of the earth's surface; the fall is due to gravity.

 

[Speedo66]

Gravity affects every object. The bullet is falling the moment it leaves the barrel.

 

[JWF III]

Heron has the best idea to prove the ballistically challenged mind wrong. But it would be hard to prove via computer. If they won't admit to basic physics, they won't admit that you did a fair test.

It's hard to use basic reasoning to prove anybody (that fully believes something) wrong. The antis are good proof of this.

BTW, I've been in (about) the same conversation with a friend that I hunt with. But he believes that all bullet fall (as they do) from the muzzle, except the .223. I chalk it up to some Army brainwashing from the 60s (when he was in). I've since quit trying, it'll never happen.

Wyman

 

[Oro]

thanks to my fiances father who CREATED Modern Ballistics, a ballistics calculator

Uh, your betrothed's dad was born 2,000 years ago? Because the physics of ballistics have been pretty well known since then. Ever since Greeks learned to throw things in combat and their talented mathematicians studied them. The physics are not complicated (they are Algebraic, not quantum), and are taught to all students in physics 101 in college...

The barrel is straight, and so is the flight path.

No, the flight path is ballistic. It reacts to the energy and angle of the launch, and then is immediately affected by gravity. Thus... ballistic. In a vacuum, it would be straight, but on earth, gravity grabs it immediately and deflects it downward. I think Expvideo understands it, but the explanation wasn't crystal.

The optic or iron sights are pointed ever so slightly at an angle so that when you are looking through the optic, you are tilting the gun slightly up. that is why the bullet arcs.

This is entirely dependent upon the range you are sighting at. In most handguns, the sight angle is set so the barrel is DOWNWARD, not up, at the moment of firing. This is because recoil pulls the firearm upwards. The longer the barrel, the more the firearm is displaced upward vs the aiming point, and the more you have to depress the sight angle to compensate for it.

There are many variables in ballistics, and the sighting plane is unique to each firearm, it's recoil characteristics, and the range it is sighted "in" for, but there are a few constants:

1) Gravity acts on all projectiles
2) to hit a close object, put the barrel below your line of sight so the upward recoil cancels the gravity and you hit where you looking.
3) for distant shots, you point the barrel very high relative to your line of sight (aka, "hold over") so you hit it as the projectile falls on it's downward arc.

 

[taliv]

while it's probably not technically the answer to your question because it requires a crosswind, it is possible. google "magnus effect"

edit: or better yet, search the archives here

 

[Regen]

In a vacuum, it would be straight, but on earth, gravity

Not quite. Gravity and Vacuum have nothing to do with each other. Gravity is due to the mass of the objects. Even in space, gravity is not zero, hence the earth does not fly away from the sun.

Vacuum relates to gas pressure (or lack of gas pressure). In a vacuum you would have no drag, thus the bullet would not slow down due to drag, but the slowing bullet doesn't cause a bullet to fall, gravity does. If you had an atomosphere but no gravity, the bullet would slow down and stop, but not fall. It would just hang there.

If you want to read an interesting book (fiction) about an environment like this read The Integral Trees by Larry Niven.

 

[NavyLCDR]

A man sitting in a tree shoots a rifle exactly parallel to the earth and at the exact same time his watch falls off his wrist. Which object will hit the ground first, the bullet or the watch? This was an actual exam question on the qualification exam for the Navy nuclear propulsion program.

 

[Mello]

NavyLT

A man sitting in a tree shoots a rifle exactly parallel to the earth and at the exact same time his watch falls off his wrist. Which object will hit the ground first, the bullet or the watch? This was an actual exam question on the qualification exam for the Navy nuclear propulsion program.

Assuming that the watch and the bullet are both the same height above the earth and that gravity acts freely upon both beginning at the same time; the bullet and the watch reach the ground at the same time.

 

[Funderb]

even if spin imparts a type of life, there can not be nearly enough surface area of lift per weight of the projectile.

 

[Duke of Doubt]

I have a good friend, not a highly educated man but fairly well read and smart, who is convinced of this "bullet lift" nonsense, too. He's one of those types who when he gets an idea into his head is inaccessible to reason, and he won't hear anything against this idea that bullets rise like dirigibles in flight. Where do they get this idea? From those horribly misleading shooting books with the ostensibly rising bullet path (the sight/bore distinction)? High school physics alone should be enough to convince anyone against this delusion.

 

[rcmodel]

http://www.exteriorballistics.com/ebexplained/5th/30.cfm

rc

 

[TimRB]

Thanks, rc. I was ready to pull out my rubber boots to protect me from some of the ...information... floating around in this thread.

Tim

 

[NavyLCDR]

Assuming that the watch and the bullet are both the same height above the earth and that gravity acts freely upon both beginning at the same time; the bullet and the watch reach the ground at the same time.

That's the answer I put down, and I were accepted as a Nuke.

In order for the lift to be created by the bullet moving through the air there would have to be an unequal surface area on top of the bullet compared to under the bullet, since the bullet is spinning, even if there was an unequal surface area, the forces would be negated by the spin.

The crosswind idea is the only plausible way of lift being created by spin.

 

[rcmodel]

Positive yaw at extreme range on a falling & barely stable bullet, could account for some lift. (Like tipping your hand up with it sticking out a car window)

But it is not a factor at normal shooting ranges.

rc

 

[NavyLCDR]

Positive yaw at extreme range on a falling & barely stable bullet

You might be confusing yaw with pitch. I used to be a nuke, now I am an aviation maintenance officer.

 

[rcmodel]

You're right.
Pitch it is!

I used to fly model airplanes and knew all that stuff.
But the mind is the second thing to go!

rc

 

[jackdanson]

Wow, glad to know the military is so well educated in these things.


Bullets are the same shape all around, there is no way for them to create lift... the bullet would have to be wing shaped; something that is round or the same shape on all side won't create lift. If it created lift on the bottom, it would create "lift" on the top, canceling it out.