Rifled barrels for spherical projectiles?

The critical factor is the location of the centre of pressure, which depends on the flowfield structure, which in turn depends mainly on the bullet's speed (supersonic or subsonic), but also the shape, air density and surface features. If the centre of pressure is ahead of the centre of gravity, the effect is destabilizing; if the centre of pressure is behind the centre of gravity, the effect is stabilizing.
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With a perfect sphere, both the center of gravity and the center of pressure are located together in the exact middle of the sphere, whether the sphere is rotating or not. In fact, since the center of pressure can never be ahead of or behind the center of gravity, the traditional meaning of "stabilization" as it applies to things like missiles and darts doesn't really apply to spheres. By the traditional definition, a flying sphere is neither stable nor unstable, regardless of spin.
 
No ball that comes out the muzzle is round. While we can load a round ball,
we do not shoot round balls. All the round balls I shoot in rifle and pistol,
come out a enlogated bullet.
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I dunno what you do to your rifle balls to elongate them but mine stay round till they hit something.

They must be spun to stablize for accuracy.
This has been known for hundreds of years.
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Then why do smoothbores work so well within their range.
 
Yes indeed smooth bores shooting round balls work good to 100 yds. A
slightly enlongated ball spinning works better. That's why rifles are more
accurate than smooth bores. This goes way back in history. In my .450
measured bore rifle, I load a .457 round ball. The extra .007 of lead has to
go somewhere when you load it so the ball becomes enlogated when it is
pushed down the bore. This provides a good surface for the rifling to be
pressed into the ball. All the bench shooters at the Nationals at Friendship
shoot this way. Same thing when loading a revolver. You do not want to
shave a ring of lead off the ball when you load it. You want that ring on the
ball for more bearing surface. I have the mouth of the chambers champerfed
so as to swedge the ball into the chamber and it becomes enlogated.
Hope this helps.
 
I use patched balls in my .54 Hawken and revolver chambers are bore size or larger. Most of mine have been bore size. So shaving lead doesn't hurt anything. The way I see it is having a revolver shave lead helps because you have a flat place on the ball for more rifling to grip.
 
It boils down to answering the question about how much better could round ball performance be from a smooth bore if only the balls were more round?
Does anyone think that the performance of a slightly more perfectly round ball would improve enough when fired out of a smooth bore to exceed the performance of one that was fired from a rifled barrel?
I don't think that there would be a quantum leap in round ball performance that could make up for that much of a difference.
The best way to find out otherwise is to find a way to actually make it happen.
 
Another important consideration that I don't know the answer to is "how much spin does a round projectile have when fired from a smoothbore, and what direction is the spin?"

If a ball fired from a smooth bore has some amount of random spin just from imperfections in the ball/bore/etcetera, then that might cause problems from the Magnus effect or similar aerodynamic effects.

Spinning the ball around an axis parallel to the direction of flight (like the spin imparted from a rifled barrel) won't cause a Magnus effect unless there's also a crosswind, but a ball spinning about either of the other two axes (pitching or yawing) will cause a Magnus effect even without a crosswind. For instance, if the ball has a backspin, it will experience an upward force as it travels downrange. If it has a topspin, the force will be downward.

It may be that the benefit of rifling with a spherical ball comes not from a stabilizing effect of the rolling spin, but from the fact that it gives the ball a predictable, repeatable spin, rather than a potentially random spin each time the rifle is fired.
 
What you say makes sense but I don't think a smoothbore has random spin from shot to shot. If they did they wouldn't be as accurate as they are within their given range.
 
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Entirely possible. In any case, I don't think it will ever be possible to experimentally answer most of my questions, because it's impossible to impart a spin on a perfectly round projectile without deforming it (since it has to deform to engage the rifling grooves.)

I got to thinking about this mostly for two reasons:

1) I see the simplified version of the Greenhill formula trotted out here all the time, but I suspect that if you look at how Greenhill actually derived the full version of his formula, he's assuming the projectile is cylindrical (longer than it is wide.) Once I get my hands on that article I found, I'm going to see if that's the case, and if it is, I'm going to re-derive the formula using the moment of inertia equations for a sphere rather than a cylinder. This may cause some terms to cancel out entirely and may change the final version of the formula.

2) I don't think that the traditional notions of "stability" apply to round projectiles, since a round projectile's center of mass and center of pressure are always co-located with each other. As such, I dont think they can be "stabilized" or "destabilized" under the traditional definitions.

I'll post any interesting results, but I realize that the simple truth is that even ball projectiles do better from rifled barrels. I'm just trying to figure out if that's because there's some inherent physical benefit to spinning a sphere in flight, or if it's just because the projectiles aren't perfectly spherical when they leave the barrel.
 
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Proof is in the freezer.......

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Scott, just looking at the way that my revolvers work, the balls are not spherical once they're loaded - and they get even more deformed when they're shot.

That .457" ball goes into a .450" cylinder, then .440" lands. It's not a sphere when it comes out of the muzzle. Oh, it's not elongated like a contemporary bullet, but it's longer than it is wide.

Also, a sphere can behave like a gyroscope. With sufficient angular velocity, the sphere will resist torques along its axis - which tend to keep it moving along a straight path (this is an enormously simplified statement of what's happening, of course).

And, just ruminating here, I'd think that another factor that is required for outside forces to act upon projectile is time. A bullet isn't in the air for all that long before it either strikes a target or the ground.

But I'm no expert on the subject - I work with electricity; I play with bullets!
 
Engaging the rifling

The most salient point yet is that the round ball is going to have to engage the rifling to test the theory, therefore it would deform the roundball.

I was thinking a round ball made of depleted uranium, and lands and grooves machined out of titanium or even diamond edged lands ...

And then I saw that really fine flintlock and thought about all those steaks, and stews and burgers and backstrap ... and raided the refrigerator!

Just a giggle that comes to mind. We print out targets we download from friends over the internet ... at which we shoot smoothbore flintlocks ... that tickles me to no end.
 
If you have a polished tungsten carbide ball accelerated by uniformly compressed air out of a polished barrel into vacuum, I'm pretty sure the stabilized and unstabilized balls perform identically. In a real world scenario you are having a lot of imperfections and non-uniformities to deal with, and you need to average out these effects by rotation.
As for the golf ball dimples, the reason a golf ball performs better with dimples than without (by about a factor of 2 - 3 distance wise) is due to the speed regime. Usually, a sphere will have nice laminar flow around it right up to midpoint, where the laminar flow leaves the surface, and the resulting turbulence generated drag. The little dimples on the golf ball produce a small layer of turbulent flow on the surface (little more drag) but allow the laminar flow to stay close to the ball for most of its length (much less drag). Unfortunately that only works in the 150 - 250 ft/s speed range, too slow for bullets to be useful.
 
The most salient point yet is that the round ball is going to have to engage the rifling to test the theory, therefore it would deform the roundball.
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Not with a patched ball out of a rifle.:D
 
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