Round Ball in Flight

[GregLaROCHE]

What happens when a patched round ball comes of the muzzle of a smooth bore? Does it just stay in the same position as loaded? Does it rotate at all? Tumble? Have there been any high speed videos put online showing what happens ?

Thanks

[bmortell]

the only place I could think to look would be taufledermaus that's pretty much all he does is film different shape projectiles

[SSGOldfart]

How would you know if it tumbles, patch should fall shorty after leaving the muzzle.

[RED BEAR]

I have no way to prove it but i doubt it just flies without moving .i think that some rotation would occur just due to air resistance.

[phonejack]

Since smoothbores don't have rifling I would say no. That's why Forster type slugs have fins to induce spin.

[john.k]

I have read the results of the Springfield tests of 1853/54 ,and the baseline was the best accuracy obtainable with a roundball from a smoothbore.......using a machine rest..........anyway ,it seems they concluded around 6 to 8" at 100 yds was possible.,but that wasnt the issue......which was range......the roundball fell away badly well before 200,whereas the rifled minie was good for 1000yds......Now I have never got anywhere near 6 to 8 at 100 with a roundball from a smoothbore ,yet I often hear claims of 4" groups at 100Yds....The ball must be a perfect sphere ,otherwise it is pushed to one side continuously..

[charlie b]

The roundball will move based on deformation and defects to the profile, eg, if the sprue is off center it will cause slightly different drag on one side or the other. Same with any 'dimples' such as those made by a patch or during the trip through the bore. Deformations at the sides of the ball will have more effect. Those at the very front (stagnation point) and at the rear will have little effect.

Also, spin stabilizing negates most of the effects of small scale turbulence in the atmosphere. Without the spin every small bit of turbulence will move it a bit.

So, if you launch a perfectly round ball in still air it will travel in fairly consistent manner.

FWIW, this is related to a knuckle ball in baseball. In that case the stitching on the ball creates off center drag, which makes the ball move randomly. Most are thrown with just a slight amount of spin so the stitching 'moves' making the ball behave even more erratically.

[GregLaROCHE]

That’s interesting about comparing a round ball to a baseball. I’m just getting into smooth bore and want to learn as much as I can about what happens and how it all works. I’m looking at fifty yards.

What difference due powder changes make, if any on accuracy? Is it still all about barrel harmonics or does it play another part in accuracy with a round ball?

[bmortell]

I agree with Charlie everything in the internal ballistics and profile would have to be perfect for no spin and any amount of non perfect will cause spin. that may be what causes the 6-8 moa limit is tiny amounts of spin in random directions will cause the magnus effect which would change its course slightly

added: maybe in theory if the gun caused the same direction spin everytime, say the bore was all polished except the last inch or 2 of the top. then you could get a top back spin evertime which could help accuracy, and the magnus effect would slightly counteract bullet drop too. disclaimer, im making this all up in my head and I don't have a way of testing it

[T_McD]

Not to mention your “roundball” isn’t round. I have seen slow motion paintball, I imagine the effect would be similar. One could coat half the ball in powder coat and use a high speed camera to test it out!

[RogerDat]

Since smoothbores don't have rifling I would say no. That's why Forster type slugs have fins to induce spin.

The Foster slug spin is really slight https://www.youtube.com/watch?v=jRPo19DWlZY it does a little something for stability but the fins are essential to make sure the slug will be able to compress as it goes through a choke.

According to that video the slug picks up the spin it does have in the barrel since airflow off the nose would put the "fins" out of the airflow. I do wonder how the minor variations in bore diameter would impact that.

[john.k]

The best shape for a subsonic roundball is a sphere with small dimples,and masses of data exist on this shape ,as its a golfball......And anyone who has ever hit a golfball can tell you,any spin will make the ball veer in the direction of the spin....Roundballs dont need stability,so rifling simply evens out surface defects with axial spin

[Tom_in_AZ]

My uneducated guess is that there would be some sort of rotation. The air flow would have to be the exact same all the way around for it to remain completely still. I would assume there would be some sort of slight rotation, but not enough to stabilize it.


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[Harter66]

: maybe in theory if the gun caused the same direction spin everytime, say the bore was all polished except the last inch or 2 of the top. then you could get a top back spin evertime which could help accuracy, and the magnus effect would slightly counteract bullet drop too. disclaimer, im making this all up in my head and I don't have a way of testing it .

In paint ball guns they call it hop up . It's done with several methods but the gist of it is the top of the barrel extension is roughed or flattened and induces back spin . In the PB guns the back spin infact flattens the flight and extends range about 25-35% .

[northmn]

I built a "smooth rifle" a few years ago. It is a 20 ga smoothbore with sights and a rifle lock. Not legal in any matches but they did exist. It would give groups of about 3" at 75 yards if one really paid attention to detail. As has been mentioned, round ball are not truly round, mine are off a bit if miked. Still I loaded it sprue out, parting line up and marked it so that it was the same side up. Loads were about 100 grains of 2f. Note I had rifle sights, which will permit one to shoot a bit more accurately. I built the gun to hunt small game and deer up close and used shot in it a lot. It would probably cover a car door at 25 yards with shot but it was kind of fun.

DEP