Recent content by Jim Boatright

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

    Yes, we want Dan Warner to make the Mark IIB ULD bullet in 375-caliber next. They should weigh 335-gr and have a BC(G7) of 0.480.
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    The new 33XC & 37XC cartridges designed by David Tubb

    My recommended initial Sg of 3.0 is based on damping out any significant initial bullet yaw as quickly as possible during the bullet's highest-drag early flight. In David's case, I believe that he was able to fire these new bullets without them having "significant initial bullet yaw" when they...
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    The new 33XC & 37XC cartridges designed by David Tubb

    Don Miller's VLD algorithm calculates an initial Sg of 2.2362 for David's MV versus 2.1954 from Bob McCoy's McGYRO program. The VLD algorithm slightly overestimates Sg for ULD bullets. I just use it for a "sanity check." My new Sg algorithm estimates an initial Sg of 2.1774 for this 245.3-gr ULD...
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    The new 33XC & 37XC cartridges designed by David Tubb

    David Tubb test-fired my latest Mark IIb copper ULD bullets in 338-caliber two days ago. These new bullets weigh 245.3-gr and have a larger (0.3386-inch OD) rear driving band and 0.125-inch base-drilling for better gas sealing. The base of the ogive is machined convex at 0.936-caliber radius for...
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    The new 33XC & 37XC cartridges designed by David Tubb

    MidSouth is accepting backorders for VV-N570 and the new VV-N565 powders. I just (back-)ordered 4 pounds of each for our 338 LM testing of 245.3-gr copper ULD bullets. Dan Warner made these Mark IIb 338-caliber ULD bullets with 0.3386-inch rear driving band OD, convex radiused bases, and...
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    Hyper Stabilized Bullets - Jim Boatright

    AB and other point-mass ballistic solvers expect you to input a BC value adjusted for the initial gyroscopic stability of your bullet. Getting initial Sg up to about 3.0 seems to produce hyper-stable flight (with minimum coning angle-of-attack) very early during the highest-drag portion of each...
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    Hyper Stabilized Bullets - Jim Boatright

    I believe that was Byron (or Byrom) Smalley who worked with Mic. He is gone now, but IIRC he had retired from Aerojet-General where he was a solid fuels expert. They were trying to approach the thermodynamically ideal spherical case shape which has a minimum surface area enclosing any given...
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    Hyper Stabilized Bullets - Jim Boatright

    Yes, it is, Lynn, along with By Smalley, who was a rocket fuel engineer. Mic as a widely published firearms author and lives in Cortez, Colorado. He likes shooting eggs at 500-600 yds with 20-caliber bullets fired at 5,000 fps. He also specializes in lever-action rifles. He is going to help me...
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    Hyper Stabilized Bullets - Jim Boatright

    I did utilize the BRL studies of the separate drag effects of various circular-arc headshape parameters, meplat size, boat-tail angle and length, and driving band size in designing my monolithic copper ULD bullet shape. However, any projectile design must be a compromise. My ULD rifle bullet...
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    Hyper Stabilized Bullets - Jim Boatright

    That CMa (CM-alpha) parameter is the overturning moment coefficient which is used in classic aeroballistics. We do not know its value for your bullet, so do not try to calculate Sg from that textbook equation which falls out of the differential Equations of Motion for any spin-stabilized...
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    Hyper Stabilized Bullets - Jim Boatright

    No, I cannot recommend anyone, gnochi. Now that Ken Oehler has come out with his lower-cost System 89 ballistic measuring system with long-range capability, many more people should have access to reliable BC measurements. Measure at the range where the distance/time-of-flight is about Mach 2.5...
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    Hyper Stabilized Bullets - Jim Boatright

    First, I always enjoy talking with another engineer., gnochi. Second, a straight 6-inch twist would have been fine for 30-caliber half-hard copper bullets. The 6-inch twist rate is too fast for using jacketed, lead-cored bullets anyway. 1. I would like to know how your BC(G7) at this...
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    Hollow boat tail bullet?

    I am taking delivery this week of a new batch of 338-caliber monolithic copper bullets CNC turned by Dan Warner to my design. They will be base drilled using a 0.125-inch drill to 0.400-inch depth, just more than half way through under the rear driving band. The base drilling has only the...
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    Hyper Stabilized Bullets - Jim Boatright

    Yes, I think I can help with that question, JB. In hyper-stable flight, the bullet is flying with the minimum possible coning angle (alpha) of less than 0.1 degree. This angle is increased during each half of a coning cycle by just the small downward change in its flight path angle due to...
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    Hyper Stabilized Bullets - Jim Boatright

    Not quite true, Flyer. The gyroscopic stability (Sg) of the flying bullet at any time in its flight is basically a function of its current spin-rate squared (P^2) divided by a function of its current aerodynamic overturning moment (4M). The overturning moment M is modeled as inherently...