Spin - Lift - Drift

FISMA

I was always under the impression that an object, such as bullet, that is rotating does not, in and of itself cause lift. This appears to make sense since if one side of the rotational motion is causing lift, the other should be doing the opposite. From Physics - it would be that the sum of the Forces on the bullet due to the air would be zero.

However, I was watching a show about American Snipers in the Gulf the other night. There was [I believe] a Marine engaging targets within 1500yards.

I remember him stating something to the effect of spin drift. He appeared to say that the spin of the bullet caused a motion up and to right, as viewed from the shooter.

I do not think he was trying to talk about a Coriolis effect either.

Has anyone heard of such a thing?

I understand that all objects fall at the same rate in a vacuum - a dropped bullet hits the ground at the same time a horizontally fired one clears the barrel. Additionally, I understand the spin stability and fundamentals of gyroscopes. However, what he said has got me wondering.

Anyhow, if you have any idea, please advise.

Also, please note that I will be using this as an excuse the next time I miss a fox or a deer.

Slan

Sparks

There is an effect called the Magnus effect that can generate forces perpendicular to the axis of spin of the bullet, but it's generally random in magnitude, varies depending on the direction of the wind, and isn't something we ever have to worry about. It's really only important in Golf, I'd be somewhat surprised if it was that important in long range shooting.

As to Coriolis effect, that won't ever affect the trajectory of a bullet. It's too small a force. It needs long time frames to effect measurable change. So you see it affecting hurricanes because it can operate on them for weeks; but anything that happens on a timescale of a minute or two with reasonable masses is way too much for it to affect.

Sparks

FISMA wrote: »

I understand that all objects fall at the same rate in a vacuum - a dropped bullet hits the ground at the same time a horizontally fired one clears the barrel.

That also happens in air, btw. Mythbusters had a rather excellent experiment showing it in action using 9mm rounds and high speed cameras:

https://www.youtube.com/watch?v=D9wQVIEdKh8

Rovi

The phenomenon described is known as 'Gyroscopic Drift' (or 'Spin Drift'), and it does indeed have a significant, measurable, and predictable effect on conventional firearm projectiles at conventional 'long ranges'.

Here's some light reading on the subject:
http://www.appliedballisticsllc.com/index_files/SpinandCoriolisDrift.htm
http://en.wikipedia.org/wiki/External_ballistics#Gyroscopic_drift_.28Spin_drift.29

FISMA

Sparks and Rovi,
Thanks for the time, clips, and links.

I will search YouTube to see if I can find the clip. Perhaps, I am mistaken, however, I would have sworn that my attention peaked when the soldier being interviewed implied lift.

I could see how there would be some curve involved with spin stability, like a curve-ball.

Thanks again

Tackleberrywho

FISMA wrote: »

Sparks and Rovi,
Thanks for the time, clips, and links.

I will search YouTube to see if I can find the clip. Perhaps, I am mistaken, however, I would have sworn that my attention peaked when the soldier being interviewed implied lift.

I could see how there would be some curve involved with spin stability, like a curve-ball.

Thanks again

Heres is my curve ball.
it the scope is canted a fraction of a degree left or right. (if we want to be technical a few minutes or seconds)
Will the round travel in a Theta axis which could cause the curve ball effect.

The reason I think this is as follows.
Some shooters use spirit levels to level cant of scope.

However a spirit level is not the most accurate way of leveling an object as it is a visual reading.
A laser leveling system would be more accurate.

So if the scope is canted left or right could this cause the trajectory to curve in th etheta axis, for lack of better terminology?

Extreme long range shooting in my opinion will show any very subtle inaccuracies in machining of a firearm or alignment.

Just a whacky 3:32am theory :D

pedroeibar1

Tackleberrywho wrote: »

Extreme long range shooting in my opinion will show any very subtle inaccuracies in machining of a firearm or alignment.

Such erudition and profound thinking :rolleyes::rolleyes::rolleyes:
P

harmoniums

Magnus effect only comes into play when theres a cross wind, and then it can either be a lift or drop depending on if its left to right or right to left.

Tackleberrywho

pedroeibar1 wrote: »

Such erudition and profound thinking :rolleyes::rolleyes::rolleyes:
P

Well it was 3:32am P.

I got to talk through and figure out the process today with a fine shooter and a gentleman
he explained all to me in a pleasant and friendly way.

Cost nothing to be nice