Why do bullets rise?

[Dfariswheel]

Here's an experiment I tell people to try to illustrate how bullets and guns work:

Go out in the yard and hook up the garden hose. Turn the water on and point the nozzle directly at a "target" 10 or 15 feet away.
The instant the water leaves the nozzle it starts falling.
The water will not hit the target, it'll hit well below it, often into the ground between you and the target.

Now point the nozzle up in the air until the water stream hits the target.
The nozzle will be pointing up in the air above the target but the water will drop onto the target.

Bullets work the same way. The instant it leaves the barrel it starts falling.
You have to point the barrel above the target so the bullet will fall onto the target.

 

[Art Eatman]

Eagle0711, just because a guy can shoot doesn't mean that he's correct about every factor involved. He was wrong about rise and fall, at least insofar as he worded his statement.

it might be possible that the rate of fall in following the arc of the trajectory might be a wee tad less without the aerodynamic effect of the rotation, but not enough to worry about. Very slightly flatter trajectory, but only very slightly. Similarly, any pull to the side would be more than offset by even a mild breeze.

 

[SRH78]

The spinning of the bullet doesn't cause it to go right, left, or any other direction. What it does is stabilize it. The reason a softball or baseball curves is because the side spinning forward creates more resistance/air pressure on that side while the side spinning the other way causes less. This is the same principle as the shape of an airplane wind creating lift. This causes the ball to "break" or curve. With a spinning bullet, no part of the bullet is spinning forward. It is simply rotating so there is no one side of the bullet, left/right/up/down, that has more or less air pressure than another so there is no reason for the bullet to drift/curve because of the rotation. The rotation is what stabilizes the bullet just like the wheels, tires, and engine of a motorcycle stabilize it the faster they spin. Remember riding your bike as a kid? Going slow, it was easy to fall but going faster you could even take your hands off the bars with no trouble. With a motorcyle and higher speeds, the effect is more pronounced. At extremely high speeds, it takes a lot of effort to make it turn. It is the same with bullets. When spinning fast, they are stable but if they don't spin fast enough due to lost velocity at long range or too slow of a twist, they destabilize and accuracy suffers greatly.

As for the story in question, I can't even imagine a soldier only trying to scare an enemy sniper who is killing our troops.

 

[mikejonestkd]

The spinning of the bullet doesn't cause it to go right, left, or any other direction.

I submit the following topics for further reading, some are dependent on a spinning bullet, but others aren't :

Magnus effect, Gyroscopic drift, Poisson effect, Coriolis drift, Coriolis effect, and last but not least - Eötvös effect

 

[rickyrick]

Howitzers point up....unless they direct fire..... its all calculated ...the scope is a simple calculatingdevice.....

 

[Art Eatman]

SRH78, I suggest that you look at the folding leaf sight on a Springfield 1903 and then explain the angle of the ladder.

 

[SRH78]

I submit the following topics for further reading, some are dependent on a spinning bullet, but others aren't :

Magnus effect, Gyroscopic drift, Poisson effect, Coriolis drift, Coriolis effect, and last but not least - Eötvös effect

Magnus effect is exactly what I described as causing a baseball or softball to curve. Imo, and based on what I have read, it would take a significant amount of wind for this to have much effect. It certainly wouldn't be anywhere remotely close to what the above story describes. One thing I haven't seen mentioned in anything I have read is the effect that more and deeper grooves in the rifling would obviously have on increasing this effect. Just something to think about.

Poisson would have the potential to cause the bullet to fail. It is fairly well known that you can actually cause a bullet to fail with too much velocity and rotation. This wouldn't pull the bullet in any given direction though. This is basically a fancy way of describing the effects of centrifugal force. A good example would be watching the tires on a dragster.

Coriolis and Eotvos effect don't have to do with the bullets rotation but rather the earths rotation.

Gyroscopic drift is an interesting concept. The logic in what I have read so far is flawed but the concept is that as gravity pulls down on the nose of the bullet, the bullet is no longer straight but becomes pointed in the direction of rotation. The result is that the bullet drifts to the side because it is no longer straight. In what I have read so far, the same very bad example keeps being used. They keep talking about a top that is spinning clockwise and that if you push on it, it will move to the right. Well duh That is simply momentum and friction at work and has nothing to do with a bullet in flight. I am not dismissing the theory but whoever came up with the top as an example didn't think it through very well.

All in all, interesting reading.

 

[SRH78]

SRH78, I suggest that you look at the folding leaf sight on a Springfield 1903 and then explain the angle of the ladder.

I assume you mean that the center of the rear sight shifts slightly to the side to account for this drift? I am a sceptic but I would enjoy taking a look at one.

 

[Art Eatman]

Yeah, the rotation does cause some drift. You can illustrate this for yourself quite easily. Take the cardboard tube from a roll of paper towels. Hold it in the middle so that you can toss it with a rolling motion. From the viewpoint of an observer on your right, first roll it out clockwise and observe the motion. Then, counter-clockwise. The first will fall rapidly. The latter will float. If you could somehow push it out without rotation, the path would be different.

 

[hornetguy]

As for the story in question, I can't even imagine a soldier only trying to scare an enemy sniper who is killing our troops.

What the sniper said was that at that extreme range, he held no hope of HITTING the guy, but was hoping to simply suppress him... make him take cover, if nothing else. Then he hit him. The sniper was astonished. I imagine the bad guy was, too.

 

[SRH78]

hornetguy, thanks for the clarification. That makes a lot more sense.

Art, what you are describing with the cardboard tube is correct but is an example of Magnus effect which is what causes a curveball to curve. So long as the bullet is pointed in the dirrection of travel, this will not cause it to drift. What it will do is cause a slight change in the rate of drop when a sidewind is present. Gyroscopic drift is entirely different. Based on what I read, it is the result of gravity applying force to the front of the bullet and pulling the nose down so that the spin axis stays aligned with the trajectory, vertically anyways. Supposedly, this causes the bullet to angle slightly toward the direction of rotation. Obviously, if the bullet is angled to one side, it will drift in that direction. The theory would be very simple to demonstrate if a long enough indoor range were available because if correct, the amount of drift would not be a linear increase as distance increases.