Basketballs and ballistics

[230RN]

From a private communication with another member:

https://www.youtube.com/watch?v=QtP_bh2lMXc

Very interesting, ballistically.

It is said* that that's why unrifled, unspun round ball muzzleloaders were so inaccurate.  Air would pile up on one random side or another on an unspun ball and push it in one random direction or another.  The video claimed that the unspun ball fell straight down, but it didn't, it swooped off to the right quite substantially.  This could have been wind, but additional trials might have shown it to be diverted in a random direction.

On the other hand, a ball with any spin at all would not be subject to this effect, and any "pileup" of air on one side or another would be impossible.  Therefore, the ball would be deflected in a predictable way, enhancing the consistency of its impact point.  (Even with the Magnus effect operating.)

The same authoritative source* says that the origin of rifling possibly began with the observation that a bent-barreled smoothbore firearm shot with increased accuracy since the ball exited spinning in a consistent direction from the bent barrel.

Further, and much later, developments of this concept resulted in what we now call rifling, although much of this development was due to the need to stabilize elongated projectiles rather than round balls.

Terry, 230RN

* Source, a fascinating, easy reading, and informative book: https://www.amazon.com/Gunpowder-Alchemy-Bombards-Pyrotechnics-Explosive/dp/0465037186

[The book] brings together a rich terrain of cultures and technological innovations with authoritative research and swashbuckling style.

[Scout26]

RC Airplane using the Magnus effect:

https://www.youtube.com/watch?v=K6geOms33Dk

[230RN]

^
I'm not sure that was a true Magnus effect.  More like mercilessly thrashing the air downward and getting lift due to the reaction.

More obviously a true Magnus effect, although the OP meant to point out how any spinning could increase accuracy of a round missile, rather than re-prove the Magnus effect:

https://youtu.be/hlmvHfIAszo

Even more driftily, after multiple painful personal lessons, I learned (A) never cut toward yourself; and (B) always use the shortest blade length in a box cutter as you can.  Even if it's just foam. :)

Terry

[K Frame]

I wonder what kind of weird wind forces were being caused by the shape of the dam itself?

[HeroHog]

RC Airplane using the Magnus effect:

https://www.youtube.com/watch?v=K6geOms33Dk

Watched several of his vids and wound up following him. Thanks! 

[freakazoid]

Need to test the muzzleloader theory in a big vacuum chamber.

[AmbulanceDriver]

Need to test the muzzleloader theory in a big vacuum chamber.

Or a spherical chicken.

[Perd Hapley]

I wonder what kind of weird wind forces were being caused by the shape of the dam itself?

Why so ortho-normative? Wind direction is a spectrum...

[KD5NRH]

Need to test the muzzleloader theory in a big vacuum chamber.

Needs to be completely frictionless, though, which makes imparting spin difficult.

[230RN]

I wonder what kind of weird wind forces were being caused by the shape of the dam itself?

That's why I wanted to see repetitive tests of an unspun ball, or at least a quick verbal report of repetitive tests.  However, the spinning test showed dramatically different results, including the fact that apart from curving away from the dam due (presumably) to the Magnus effect of the rotation, it stayed in a pretty straight line, perpendicular from the dam face.

This confirms the notion that any spin will reduce the random flight of an unspun ball.  Bearing in mind of course, that a dropped basketball has considerably less sectional density than a lead ball, and doesn't drop at firearm velocities.

I'm aware of the time limitations of most online videos, so extensive descriptions are sometimes not practical.  All in all, it was a good experiment, but it was a demo of the Magnus effect, not of the effect on accuracy of a spinning projectile compared to a non-spinning projectile.  Or at least they ignored that aspect of it.

It's possible that being firearms-challenged Australians, the ballistics / accuracy part of the experiment didn't even occur to them.

Terry, 230RN

REF:
Hatcher's Notebook, "Rifling," p 555 ff.

Even if the ball should be a very tight fit in the smooth bore [exiting with no rotation at all] ... a small pile of compressed air may be pushed along by the ball until something causes it to deviate to one side a sight amount, when it may "break" from its former path...

(Elisions and insertions mine.  He later implies that this rotation needs to be on the axis of travel, but while desirable, this is not necessary to obtain some improvement in accuracy.)

[bedlamite]

(Elisions and insertions mine.  He later implies that this rotation needs to be on the axis of travel, but while desirable, this is not necessary to obtain some improvement in accuracy.)

Try shooting a rubber band with one side stretched more than the other. It imparts a spin and shoots farther and more accurately than one with both sides equally stretched.

[HeroHog]

...and it stings a bit more when it slips off your front finger and pops ya in the face.

[230RN]

I've got a smoothbore propane-powered pistol which has some gizmo in the barrel which imparts an adjustable horizontal spin on the plastic 6mm BB.  That thing is extraordinarily accurate out to about 50 feet, despite how light the plastic BBs are.