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Old April 14, 2010, 12:46 PM   #28
ScottRiqui
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Join Date: January 27, 2010
Location: Norfolk, VA
Posts: 2,905
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.

Last edited by ScottRiqui; April 14, 2010 at 12:59 PM.
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