CSI and bullet trajectories

[fisherman66]

Gary M,

You are flat wrong. Drag determines the orientation of the bullet. The increased surface at the rearward portion of the projectile will cause it to lag.

 

[Sergeant Sabre]

I've thought about this from time to time. I think the bullet would be oriented nose-down.

Ever seen a hail-mary throw in a football game? The ball pitches nose-down as it arcs through it's tragectory, no matter how nice a spiral-throw it may be. I think it's the same principle.

 

[Sam]

fisherman,
you're wrong.
Drag has some influence but gyroscopic stabilization can easily make a bullet stay in the same attitude throughout the flight.
A 1-10 twist applied to a 175 gr bullet will ensure that it maintains the same attitude throughout the flight, to over 1600 yards A 1-12 twist will allow the same bullet to "go into trail", somewhere around 1100 yards and often closer.

Thats why long range shooters use the absolute minimum amount of twist necessary to stabilize the bullet, so it will stay noze first. It is not at all hard to stabilize a bullet enough to keep it on attitude as opposed to in trail. When you go looking for target barrels you can find all kind of oddball twists available, everything from 1-8 to 1-14 in 30 cal just to meet the precise need to keep a particular bullet in trail.

Sam

 

[fisherman66]

The bullet discussed is not a .30 cal bullet. The distance is measured over apogee. Gyroscopic phemonenon is not an effecient action in a gaseous atmosphere, and would require the input of more energy to maintain the edge over drag. So... unless you are talking about ball ammunition (where drag is applies without orientation) the bullet will fall nose down.

If you contend that gyroscopic force is stronger than drag at apogee on a 9mm bullet at standard load, and at standard rate of twist then we will have to agree to disagree.

 

[Joejojoba111]

I think that the bullet is spun enough to be stable in air, so we agree it's stable. And since it's stable it points down when it falls because it acts sort of in an aerodynamic manner.

So yea I think if there was gravity but no air, then it would not nose-down when falling. And if over-spun it wouldn't nose-down either.

 

[Sam]

Sorry fisherman,
30 cal was used only as an example. 9mm will do the same. They are horribly overstabilized with a standard twist of 1-10" and a launch speed of approx 1200fps that gives you a rotation speed of 21000rpm more or less. She will still be spinning like a top till it hits the ground. Drag will stop forward motion long before it significantly effects rotational speed.
All you have to do to prove it is take a look at the oblong holes in the target
where the bullets went through sideways. There are very very few rounds that are not way overstabilized. That's why the specialty shooters work so hard to find those "sleeping" combinations that will keep a bullet point on all the way.

Sam

 

[fisherman66]

The bullet will actually enter a spiral nose first.

http://www.nennstiel-ruprecht.de/bullfly/fig30.htm

 

[Matt G]

Bullets do tumble after they have expended their energy, at least after having been fired at fairly high angle.

Exhibit A: My great uncle, who was killed by a chance .22 bullet. He was far away from anyone, and his mother-in-law nearby didn't hear any shot. The shot had come from an extreme distance, and the bullet was tumbling as it dropped into my great uncle's chest. The ME found that the bullet struck almost base-on. (DON'T shoot rifles in the air!)

Exhibit B: Hatcher's Notebookhttp://www.amazon.com/exec/obidos/t...bs_b_2_1/104-8603045-4928745?v=glance&s=books, by Julian Hatcher. (A must have, by the way). In the 1920's and '30's Major Hatcher was doing some really fun experiments in ballistics. Stuff like setting machine guns on piers in bays, firing them straight up, and timing how long it took for bullet strikes to be seen in the water or on the beach. On at least one occasion, a bullet struck the gunnel of a boat tied to the pier after falling straight back to earth, and barely made an imprint in the wood. The imprint showed clearly that the bullet had struck base-on.

 

[Gunpacker]

Stabilization

Well, only thing I can add is that I have seen long range bench rest match targets fired at 1000 yds, and there were NO oblong holes in the targets. Indicates to me that bullets strike nose first in normal flight. However, it may be possible that a round fired straight up will not have aerodynamic forces to nose over the bullet, allowing it to start down stabilized in a tail down attitude that would be maintained due to the spin that would still be high. In addition, I would suspect that uneven forces imparted to bullets canted to direction of flight would cause severe accuracy problems.