Well, going out on a limb here, but the Army Aerial Gunnery Manual teaches us about something called "The Vertical Plane Gyroscopic Effect." Essentially, firing off axis, in a direction other than that of the helicopter's travel, induces a crosswind. With A right crosswind, gyroscopic precession (force applied to a rapidly spinning object takes place 90 degrees to the force, in the direction of rotation) will cause the bullet to hit high, and a left crosswind would cause it to hit low, assuming the bullet is turning clockwise as viewed from its base. As far as sine wave trajectroy, I don't think so.
John
Hondo, you are not going out on a limb at all. Understanding that "gyroscopic precession (force applied to a rapidly spinning object takes place 90 degrees to the force and in the direction of rotation ) is the key to understanding long range gyroscopic spin drift. Bullets from a rifle with right handed twist will drift to the right, and bullets fired from a rifle with left handed twist will drift to the left. At 1000 yards gyroscopic spin drift can be as much as 13" in a 30-06. It is counterintuitive for most people to realize that the force applied to a bullet isn't directly in the opposite direction (i.e. 180 deg) to an applied force. Vertical drift resultant from a crosswind is approximately 1/10th of the gyroscopic side drift. The Research Lab at Aberdeen considers the effects so small the they only list it's effects in firing tables for guns over 8" bore. A stronger crosswind velocity from the forward motion of a helicopter is why Hondo would have seen them in his Helicopter firing tables. The Physics at first seem counterintuitive but they are established and proven facts. Bullets do drift at long range in the direction of the rifling twist and there is a very small vertical drift in crosswinds. Usually however the total effects are neglible compared with other external factors such as wind drift and bullet drop. And aren't enough to worry about at sane hunting and normal shooting ranges...............DJ
Remember this is all supposed to be for fun.......................
Were one to set up a rifle with the bore axis perfectly level, while also holding an identical projectile in one hand at the same height, both bullets would hit the deck at the same instant when fired and dropped simultaneously. The downward vector doesn't care how fast its perpendicular travel is; down is down.
I wondered if a very LOW BC bullet launched from a magnum pistol, would travel in an arc, but on the downhill side of the arc the drag would be great enough to slow the gravitational (constant) pull? Not exactly "lifting" it, but slowing it. Now this is probably some BS conjured up in my simple little mind, but maybe its worth a thought.
Having shot sixguns quite a bit at long range, I find that certain bullets fly very well indeed inspite of their low BC. I don't know ballistics all that well and this thread has me lost as it appears that I am not sure what everyone is talking about, but I have seen amazing things from heavy for caliber bullets fired at subsonic muzzle velocities from sixguns at real long range. I've shot some 405gr cast bullets from my Linebaugh 45 Colt starting at just over 1000fps and seen some amazingly flat trajectories to 1000 yards. I beleive these bullets and similar bullets behave themselves better than many rifle bullets when range gets way out there.
I know some sixgun shooters that could shame many rifle shooters once the distance went beyond 300 yards.
Were one to set up a rifle with the bore axis perfectly level, while also holding an identical projectile in one hand at the same height, both bullets would hit the deck at the same instant when fired and dropped simultaneously. The downward vector doesn't care how fast its perpendicular travel is; down is down.
RSY
Of course you can fight Mother Nature (i.e. gravity), Airplanes fly all the time don't they? She'll win eventually but some things can leave the ground. It's true that a perfectly horizontal bore shooting a bullet would hit the ground at the same time as one dropped at the same exact instance but only in the absense of other forces.. Airplanes fly because temporarily Lift superseeds the pull of gravity. Forces on a bullet such as crosswind spin drift could actually cause a horizontally fired bullet to very slightly impact later.......DJ
Remember this is all supposed to be for fun.......................
If you want a good understanding of drifts get a copy of "Rifle Accuracy Facts". It has the best explaination of "Wind Drift" that I have ever read. No it's not the wind blowing on the side of the bullet. Good luck!
Maybe someone already wrote this, must confess I didn't read every post.
Baseballs curve, move, or float in un-natural ways because of the seams. I haven't checked all my bullets yet, but the Noslers and Hornadys I did look at don't have any seams. I think they build them that way on purpose, to reduce drag I reckon.
[The Physics at first seem counterintuitive but they are established and proven facts. Bullets do drift at long range in the direction of the rifling twist and there is a very small vertical drift in crosswinds. Usually however the total effects are neglible compared with other external factors such as wind drift and bullet drop. And aren't enough to worry about at sane hunting and normal shooting ranges...............DJ [/quote]
The long range drift in the direction of the rifling twist was reported by Elmer Keith many, many years ago. Actually, I read it in a book or article by Keith so he probably did not "discover" this. Anyway, this type of info was apparently well known to the old military shooters when Elmer was a member of the National Guard rifle team back in the Twenties (Montana IIRC but could have been Idaho).
Once again going from memory of books read long ago so I may have some minor details wrong, but the gist is that this effect has been well known for quite some time.
Gunnery, gunnery, gunnery. Hit the target, all else is twaddle!
Of course you can fight Mother Nature (i.e. gravity), Airplanes fly all the time don't they? She'll win eventually but some things can leave the ground.
Sorry for not being more specific. We're talking about bullets, right?
Bullets are symmetrical, airplanes are not (hence their ability to create lift). Were you to install an upper airfoil the same distance above the centerline of the aircraft, with the same attitude relative to center, as the one below the centerline, the plane would not fly. The upper "mirror" wing would cancel out the lift of the lower wing, thus giving gravity the decisive upper hand.
RSY, No a bullet is not an airfoil and airplanes don't spin at over 100,000 revs per minute either. The analogy is to show that there are forces that act against the pull of gravity. In airplanes that force is lift, in bullets it is gyroscopic spin drift. The two are completely different forces but both can act in opposite direction of gravitational pull. Gyroscopic spin drift is also a minor enough force that it's rarely noticed...but it is there nonetheless...........DJ
Remember this is all supposed to be for fun.......................
Don't forget the Coriolis acceleration! It matters which direction of twist you have in your rifle and the amount of drift in the northern hemisphere compared to the southern hemisphere. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />
Sierras older reloading manual had good discussions of exterior ballistics, I presume the current editions do too.
jim
LCDR Jim Dodd, USN (Ret.) "If you're too busy to hunt, you're too busy."
Jim...Keith may have been remembering some of the Springfield 45/70 Trapdoors. The rear sight was made to accomadate this drift at long range, as the sight was made with an automatic drift compensator built in. As you moved the elevation up, the sight moved to the left. Check it out..
so gravity still exscists, but the bullet could over come its froces and be shot around the wrold right back to point it started at. youd have to watch your back on this one. i will not belive that bullet would be in the same place even if wind didnt effect it. in the dead calm that bullets spinning would more than likly make it end up miles from where where it started.
now if there was no gravity that same bullet i belive would come true and would end up right were it started. spinning or not.
but wait we now have the moons gravitational pull to deal with, hmmmmmmmmmm all to confuseing, i have no idea what im talking about, i just shoot.
I think the answer to all the above is to design a rifle that shoots apples at telephone poles. Then the telephone pole gets rotten from all the apple juice on it, topples and falls on the game, killing it. Either that or you fly an airplane through the chest cavity of a deer.
I have one question -- do you have to put a lead tip on an airplane to get it to expand, or do they make a TSX Cessna? (I guess that is two questions.)
Strange we ever hit what we're shooting at. Last time I hunted out of a helicopter, I wondered why I couldn't hit what I was shooting at. I thought it was the speed I was travelling. ;-)
"Keep thy heart with all diligence; for out of it are the issues of life." (Prov 4:23)
Harold Vaughn has proof positive that a cross wind does create lift on a bullet, for part of the trajectory. The results of his experiment are on p197 of his book (see attachment link). The image shows both horizontal displacement and vertical displacement from a crosswind. Absent lift, it is very hard to explain his results.
The fundamental rule of physics is that anything that happens must be possible. The data are never wrong. It is up to us to come to terms with the data.
Here is my attempt to reconcile with the data:
A bullet fired horizontally in a cross wind will align its axis so that the axis is parallel with the vector sum of the crosswind and the bullet velocity. The drag vector now points directly out the bottom of the bullet, and is not parallel with the trajectory. It now has a vector component in the direction of the wind. That, not the wind blowing against the side of the bullet, is the main cause of horizontal drift with wind.
Similarly, after the peak of the trajectory, the bullet will nose-down slightly, since this position creates the least drag. Again, the drag vector points directly out the tail of the bullet. Drag now has a huge rearward component, and a slight upward component--lift. But only after the peak of the trajectory.
Harold also "ran the math" to show that, at 200 yards, the lift can upwardly displace a bullet about an inch in a 20 mph wind.
Hear's what I understand about this. Bullets do drift right or left (depending on weather you're in northern or southern hemisphere) and the spin of the bullet does something to is. (I don't remember what I read very well)
This is so minimal as to not make any diference to us, but to the Navy shooting shells 15 miles it could put the shell off something like 100 yards. We, who rarely shoot beyond 1/2 mile would get near nothing in this kind of drift.
Don't worry about this. The thing is that there are so many other variables that we have to worry about that it makes no difference. We've got tiny gusts of wind, the inaccuracy or the rifle, high and low pressure places between us and the target, and a host of other things that much more difference.
True, but so small it can be disregarded.
"Among the many misdeeds of the British rule in India, history will look upon the Act depriving a whole nation of Arms as the blackest" -Gandhi
"The most foolish mistake we could make would be to allow the subject races to possess arms" -Hitler
