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  1. J

    Spin Drift

    This is all quite interesting, and I am learning a lot from these learned shooter's comments. I do have one question though. I know little about gain-twist barrels and have never used one. When a barrel maker says 3/4 gain twist, I wonder if they mean that as the ratio of the initial and final...
  2. J

    Spin Drift

    Comments added in-line in [brackets]. Jim Boatright
  3. J

    Spin Drift

    Yes, Tiro, Harry Vaughn had the CWAJ effect about right, but not having Coning Theory, he did not explain it quite correctly. I had to buy a second copy of his wonderful book about 10 years ago because I had worn out my first one. Bob McCoy also explained CWAJ and almost discovered Coning Theory...
  4. J

    Spin Drift

    The spin-stabilized bullet's yaw-of-repose (beta subscript R in my papers) is caused by two small overturning moment TORQUE IMPULSES per coning cycle, centered on the Top Dead Center and Bottom Dead Center bullet positions in that coning cycle. During each half coning cycle, the apparent wind...
  5. J

    Spin Drift

    Thanks for pointing this out, Lash. Yes, the CWAJ trajectory deflection is a one-time transient effect which depends upon the (presumed horizontal) crosswind first encountered by the bullet after it exits the muzzle blast cloud (shockwave) a few yards ahead of the muzzle. Gustavo and I expect...
  6. J

    Spin Drift

    The yaw-of-repose of a spin-stabilized projectile in flat firing is a strictly horizontal attitude bias of the coning axis pointing direction, always perpendicular to the gravity gradient which is its cause. Its vertical component is identically zero at all times. The yaw-of-repose is also...
  7. J

    Spin Drift

    Not at all, DC. In the Coning Theory and Spin-Drift papers, I explained how and why the yaw-of-repose and spin-drift occur and numerically calculated SD to within 0.021-inch (Std Dev) of the PRODAS data for each millisecond over 1.693 seconds of a 1000-yard simulated flight. I was merely trying...
  8. J

    Spin Drift

    Cranz has quite a discussion of spin-drift in high-angle firing. He says the sane things. Those high-angle effects are caused by 1) the projectile nearly coming to a halt at apogee, 2) the thinner air at flight apogee, and 3) the projectile re-accelerating as it falls. Have you ever had your...
  9. J

    Spin Drift

    Yes. All rifle bullets track up to 0.1 degrees high at reasonable ranges. The tracking angle increases with range and time of flight in flat firing. If you are asking if you can detect it, no, not very likely. At somewhere around 70 degrees of muzzle elevation you might have the problem you seem...
  10. J

    Spin Drift

    Just thought I would mention another data point. I ran Bryan's AB point-mass solver for one of my new bullets to be fired at Whittington NM later this year. I used the McDRAG calculated BC(G7) multiplied by 1.124 to agree with David Tubb's 1000-yard measurements of similar design hyper-stable...
  11. J

    Spin Drift

    Actually, the rifle's torque reaction to spinning-up a RH-twist bullet would be leftward, top side into the body of a right-shoulder rifleman and tightening a RH-threaded barrel into its receiver threads. The Brits never would say why they used LH rifling and LH receiver threads, but the...
  12. J

    Spin Drift

    No, I was referring to wood-block printing of artist's sketches for use in book illustrations, before photography was common.
  13. J

    Spin Drift

    I tried looking for "drift firings" in my standard references without much luck. The effect was first discovered (about 1800) in attempting to aim accurately with early rifled artillery and naval guns. Poisson, Magnus, and other top mathematicians and physicists attempted explanations of...
  14. J

    Spin Drift

    "Drift Firings" of rifles were all the rage in Europe in the 1870's and at Aberdeen in the '80's. Bryan Litz is duplicating them in modern times. Simultaneous firing of essentially identical LH and RH twist rifles at long-range targets with half the horizontal difference in the group centers...
  15. J

    Spin Drift

    I little historical perspective on ELR rifle shooting. I recall reading somewhere in my bookcase of Civil War military history of an unusual event which occurred late in the war in north Georgia. A Confederate sniper returned to camp one early evening with his trusty English-made 451-caliber...
  16. J

    Spin Drift

    Let me say a few words in defense of PRODAS and other 6-DoF flight simulators. These are the most sophisticated trajectory propagations available. They integrate the Equations of Motion for a projectile in very small time-steps using sophisticated numerical techniques which have long been used...
  17. J

    Spin Drift

    Please stop trying to generalize about spin-drift from a few worked examples. The next thing will be that somebody will notice that all jacketed, lead-core bullets are fired in 30-caliber rifles. I will add some hyper-stabilized examples in the next release. The spin-drift is caused by...
  18. J

    Spin Drift

    On the other hand, I am most interested in how today's best monolithic ELR bullets can be made to behave best at extreme ranges. I view application of new theory to old bullet designs as a necessary and desirable type of "backward compatibility." We have already learned what we can from them...
  19. J

    Spin Drift

    Please do not take those ill-advised generalizations which I made from a very small 30-caliber data set as gospel. All of this is likely to change when we look at initially hyper-stabilized bullets launched at very high velocities anyway. Hyper-stability had not been thought of when that paper...
  20. J

    Spin Drift

    The cone-on-cylinder model shows promise of yielding Iy/Ix value within 0.5 percent of the numerically integrated values for modern solid monolithic ELR bullets, using the bullet descriptors already being input by the user. That is exceptionally good performance for aeroballistics work. The main...
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