Recent content by Jim Boatright

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

    Yes, Pmax is very sensitive to combustion chamber volume and SS pressure in Ql which is true in real life, as well. That is why I warn tyros about playing with bullet seating depth (or "bullet jump") near a max load. Making mistakes and sometimes learning from them is called "experience." I...
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    The new 33XC & 37XC cartridges designed by David Tubb

    That's fine Gwain, as long as you just vary one parameter at a time and have a reason for doing it, such as powder lot variation. Shot-Start Pressure covers a multitude of variables in QL, which is one of it weaknesses. QL also does not consider variability of primer characteristics. I also do...
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    The new 33XC & 37XC cartridges designed by David Tubb

    In the lower left-hand quadrant of the QL display screen, I usually select a display of chamber pressure and bullet speed versus bullet position in the barrel. The bullet position at maximum chamber pressure (Pmax) is annotated as a black vertical line going through that pressure. There is a...
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    The new 33XC & 37XC cartridges designed by David Tubb

    SID, you mentioned having difficulty in FL-resizing your 33XC brass. If you are already using Imperial Sizing Die wax ("sparingly"), and your chamber and die are properly polished internally, that sounds like a minor disagreement between their dimension specifications. In my custom 338LM reamer...
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    The new 33XC & 37XC cartridges designed by David Tubb

    I find N570 to be perfect for our new 245.35-gr monolithic copper 338 bullets in 338 LM chambering. QL shows the Z1 and Pmax occurring exactly together. We are still using 10 year old Lapua-made cases with no neck turning. They have each been fired dozens of times in ladder and group tests with...
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    The new 33XC & 37XC cartridges designed by David Tubb

    These loads look very good for muzzle speed uniformity. "Gravity Drop" variation will run -2*(dV/Vmean)*total drop from bore axis at the target. You can use an "unbiased standard Deviation" for dV. For a 5-shot sample size, the "unbiased SD" is 1.118 times the SD computed in your chronograph...
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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...