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  1. J

    The new 33XC & 37XC cartridges designed by David Tubb

    I think David could have fired my 225-gr and 242-gr copper ULD bullets about 200+ fps faster than the 3378 fps and 3335 fps which he used for 1000-yd tests. We are well into the realm of "diminishing returns" here for MV versus case capacity. Any 40-degree shoulders are difficult for Peterson to...
  2. J

    The new 33XC & 37XC cartridges designed by David Tubb

    When David tested my prototype 338 copper bullets over 1000 yards, he mentioned using about 109 grains of H1000, so I knew he was not using even a 338 AI case. With the 225-gr base-drilled bullets at 3378 fps (5-shot ES=13; SD=3) his Oehler 88 measured BC(G1) of 0.794 (ES=.037; SD=.014) the...
  3. J

    Hyper Stabilized Bullets - Jim Boatright

    Gustavo and I have updated and extended our formulations for calculating yaw of repose and spin drift for long-range rifle bullets. I hope this resolves any questions about these mysterious observed aeroballistic effects. Spin Drift estimations match PRODAS 6-DoF results to within a few...
  4. J

    Hyper Stabilized Bullets - Jim Boatright

    Thanks, Theis. I feel fine now. 1. Muzzle brakes and suppressors are sort of opposites in what they do with the gases after porting them away. The most I can see for MB design is to stage the port sizes to more or less equalize the momentum harvesting from each successive chamber for effective...
  5. J

    Hyper Stabilized Bullets - Jim Boatright

    The medical exam went very well with no sign of bladder or prostate cancer. Here is an edited, corrected, and more readable version of that Rifle Bullet Stability paper:
  6. J

    Hyper Stabilized Bullets - Jim Boatright

    I want to distribute this new paper on "Rifle Bullet Stability" before starting some required medical procedures tomorrow. It is overly long and involves some math (mostly algebra) and physics, but should contain a few nuggets of accessible information useful to ELR riflemen.
  7. J

    Hyper Stabilized Bullets - Jim Boatright

    These are thoughtful and intelligent questions, MP, and I will attempt to answer them all, but it will require some thought and effort to do so properly. First, I will explain the rationale for base-drilling certain of my copper ULD bullets. The cost in bullet performance of removing...
  8. J

    Hyper Stabilized Bullets - Jim Boatright

    Twist rates can be generalized as "n calibers per turn" by dividing the twist in inches or millimeters per turn by the bore ID (1.0 calibers) in the same distance units. The helix angle (a) of the rifling is also an apt description of how the bullet "sees" the rifling as it is being engraved and...
  9. J

    Hyper Stabilized Bullets - Jim Boatright

    I see no reason to bother with a gain-twist barrel, especially for larger calibers. All modern rifle cartridges operate at about 60,000 psi, more or less, as a peak chamber pressure. The peak base-pressure on the bullet is usually about 90-percent of the peak chamber pressure. The peak force...
  10. J

    Hyper Stabilized Bullets - Jim Boatright

    I am glad to hear of your vote of confidence in hyper-stability, MP. By moving to a 50-percent faster barrel twist rate, you will be exploring new, uncharted territory. You will have resolved several old problems, but who can say when new problems might arise. I do not foresee any, but time and...
  11. J

    Hyper Stabilized Bullets - Jim Boatright

    The 50-caliber M2 bullet weighs only 650 grains, IIRC. It is very "short" and "fat" by ballistic standards, which allows its use in 15-inch twist-rates. Scaled to 30-caliber, it would weigh only 140.4 grains. A ballistically "proper" lead-cored 50-caliber bullet would weigh about 900+ grains...
  12. J

    Hyper Stabilized Bullets - Jim Boatright

    First, aeroballistic flight does not begin until the bullet penetrates the muzzle blast shockwave, usually about 3 to 6 yards in front of the rifle barrel's muzzle. Gyroscopic stability (Sg) is a measure of the spin-stabilized rifle bullet's ability to withstand the aerodynamic overturning...
  13. J

    Hyper Stabilized Bullets - Jim Boatright

    Subsonic flight is sirene and can be extremely low drag (Cd = 0.003 is possible). It is in the several hundred yards of chaotic transonic flight where problems arise. The boundary layer acts about the same throughout the bullet's flight. We do not fully understand what happens with different...
  14. J

    Hyper Stabilized Bullets - Jim Boatright

    The part of my reply to MP got lost where I referred him to the discussion of the "VLD accuracy problem" in my paper on Third Generation Rifle Bullet design posted here in the Resources section. That is a discussion of the in-bore yaw problem with boat-tailed secant-ogive VLD bullets.
  15. J

    Hyper Stabilized Bullets - Jim Boatright

    No, MP, the boundary layer airflow should be laminar only over the ogive of properly designed rifle bullet. The flow over the bullet shank and afterbody should be turbulent. In any case, the 3 to 5 thou depth of the rifling engraving is completely submerged within the boundary layer and cannot...
  16. J

    Hyper Stabilized Bullets - Jim Boatright

    Yes, those 50-caliber barrels should have been made with a 10-inch per turn twist-rate. The standard 15-inch twist was always marginal for gyroscopic stability.
  17. J

    Hyper Stabilized Bullets - Jim Boatright

    I have not looked in depth into rifle bullet destabilization during transit of the muzzle blast region. Perhaps others might have done so. That being said, by radically increasing the axial rigidity of the hyper-stabilized spinning bullet, any destabilization of the fired bullet should be...
  18. J

    Hyper Stabilized Bullets - Jim Boatright

    We also have at 28-inch, 7-twist, 6.5 mm barrel on order (dual-purpose 6.5/284 for 140-gr class lead-core bullets and 105-gr copper bullets). Our 7-twist 338 Schneider P5 barrel will be ready soon, properly fitted with a Light, Air-Working (LAW) muzzle brake by Mic McPherson of Cortez CO . It...
  19. J

    Hyper Stabilized Bullets - Jim Boatright

    Not much progress to report right now, MP. Dan Warner has made some solid 6.5 mm bullets, but we don't have a fast-twist barrel to really fire them from. We are awaiting a testable quantity of base-drilled 6.5 mm 105-gr bullets and a 7-inch twist 6.5 barrel for firing both these 105-gr ULD...
  20. J

    Spin Drift

    Yes, LastShot300, all else being equal, the spin-drift at 1000 yards is linearly proportional to the barrel twist in inches (or calibers). I did not expect to see that. I happen to have an elaborate spreadsheet for calculating SD at 1000 yards as published in the SD paper for eight different...
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