The Firing Line Forums Rifled barrels for spherical projectiles?
 User Name Remember Me? Password
 Forum Rules Firearms Safety Firearms Photos Links Library Lost Password Email Changes
 Register FAQ Calendar Search Today's Posts Mark Forums Read

 April 14, 2010, 12:28 PM #26 ScottRiqui Senior Member   Join Date: January 27, 2010 Location: Norfolk, VA Posts: 2,905 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.
 April 14, 2010, 12:32 PM #27 Hawg Senior Member   Join Date: September 8, 2007 Location: Mississippi Posts: 12,922 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. Last edited by Hawg; April 14, 2010 at 12:50 PM.
 April 14, 2010, 12:46 PM #28 ScottRiqui Senior Member   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.
 April 14, 2010, 03:28 PM #29 Brandy Junior member   Join Date: March 31, 2010 Posts: 151 Proof is in the freezer.......
 April 14, 2010, 04:03 PM #30 Hardcase Senior Member   Join Date: April 14, 2009 Location: Sunny Southern Idaho Posts: 1,909 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! __________________ Well we don't rent pigs and I figure it's better to say it right out front because a man that does like to rent pigs is... he's hard to stop - Gus McCrae
 April 14, 2010, 04:04 PM #31 CajunPowder Junior member   Join Date: April 1, 2010 Location: Louisiana - Cajun Triangle Posts: 223 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.
 April 14, 2010, 04:21 PM #32 mapsjanhere Senior Member   Join Date: August 6, 2009 Location: Albuquerque Posts: 2,637 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. __________________ I used to love being able to hit hard at 1000 yards. As I get older I find hitting a mini ram at 200 yards with the 22 oddly more satisfying.
April 14, 2010, 10:56 PM   #33
Hawg
Senior Member

Join Date: September 8, 2007
Location: Mississippi
Posts: 12,922
Quote:
 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.
Not with a patched ball out of a rifle.

April 15, 2010, 04:27 PM   #34
CajunPowder
Junior member

Join Date: April 1, 2010
Location: Louisiana - Cajun Triangle
Posts: 223
True

Quote:
 Originally Posted by Hawg Haggen Not with a patched ball out of a rifle.
So I'll need a kevlar patch for my DU or TC round ball ... hmmmmm

 April 15, 2010, 05:55 PM #35 Senior Member   Join Date: August 21, 2008 Location: Kansas City Posts: 1,391 I use Teflon myself
 April 15, 2010, 07:44 PM #36 mykeal Senior Member   Join Date: October 8, 2006 Location: Northern Michigan Posts: 2,772 I use pillow ticking. And so do, I believe, the vast majority of long gun shooters, rifled or smoothbore.
April 15, 2010, 11:01 PM   #37
Hawg
Senior Member

Join Date: September 8, 2007
Location: Mississippi
Posts: 12,922
Quote:
 I use pillow ticking. And so do, I believe, the vast majority of long gun shooters, rifled or smoothbore.
Likewise

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Hogan's Alley     Tactics and Training     Handguns: The Semi-automatic Forum     Handguns: The Revolver Forum     Handguns: General Handgun Forum The Hide     The Art of the Rifle: Bolt, Lever, and Pump Action     The Art of the Rifle: Semi-automatics     The Art of the Rifle: General     The Dave McCracken Memorial Shotgun Forum     NFA Guns and Gear     The Hunt The North Corral     Lock and Load: Live Fire Exercises     Competition Shooting     Curios and Relics     Black Powder and Cowboy Action Shooting The Skunkworks     Gear and Accessories     The Smithy     Handloading, Reloading, and Bullet Casting         Bullet Casting     The Harley Nolden Memorial Institute for Firearms Research The Conference Center     General Discussion Forum         TFL Photo Contest     Law and Civil Rights         Legal and Political     S.W.A.T. Magazine The Firing Line Gun Show     S.W.A.T. Exchange     Retail Deals and Feedback Forum Support     Site Questions and Tech Support (NO FIREARMS QUESTIONS)     Software and Function Testing

All times are GMT -5. The time now is 06:22 PM.

 -- vBulletin 3 ---- vBulletin 3 - variable fonts ---- Low profile (unsupported) Forum Home Page - Archive - Top