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Thread: Balck powder cartridges, long range, and the speed of sound

  1. #21
    Boolit Master
    Join Date
    Nov 2010
    there are 2 types of bullet stability.
    one is gyroscopic stability and the other is dynamic stability.
    gyroscopic stablility, sg, can be calculated, with the number 1.0 being absolute min for stability, and 1.5 being the goal for smokeless supersonic bullets at normal ranges.
    thgis stability is relevent to the spinning top.
    dynamic stability is a different cat to skin.
    even top ballisticians cannot fully understand it to this day.
    it is accepted fact that you really have to fire a lot of shots to fully eastablish data on a specific bullet at different velocities and twists.
    airflow and balance are some of the factors that come into play.
    you cannot generalize.
    keep safe,

  2. #22
    Boolit Master
    Join Date
    Nov 2010
    there exists a skin of air on the surface of a bullet in flight called the boundary layer.
    friction partly sticks this air to the bullet, and partly it is kept there by clinging to the point.
    if the point is too sharp, the boundary layer will let go, and another one will form in ita place.
    understandably, this repetitive action will disturb the bullet's stability.
    the air flowing over the bullet is not doing so in a clean manner.
    the original money bullet design called for a meplat (ball at the front of the ogive) of 50 to 55% if calibre.
    the metford bullet meplat was this or a little more.
    something to do with clean air flowing over the bullet.
    the ellipse also seems to offer clean airflow.
    transonic aircraft often exhibit one of these two profiles.
    fuel economy is a great reason to look for reduced drag.
    also there was loss of human life exploring trans and supersonic flight.
    to go super you have to go through trans, and come back through it to land safely.
    a major contributor to increasing b.c. is to lengthen the ogive.
    this is easy with jacketed bullets, because the jacket supports the nose.
    our black powder bullets have unsupported noses, allowing the nose to set back on firing, thus reducing apparrent b.c.
    if they do not do it the same each time, each bullet will have a different b.c., putting more vert in the group.
    even worse is that the setback can bend the nose moving the centre of mass away from the axis of the bullet.
    when this happens, spinning the bullet faster diminishes stability rather than improving it.
    harder alloys help here.
    my own take on this is to not have a nose as cast more than 1.5 calibres in length, and use an alloy 16:1 to 12:1.
    others differ on this and get good results.
    the ellipse is defined by a formula using 2 axes so the shape is easy to define, and the money/metford is easy to define using meplat diameter, ogive radius, and nose length.
    a pp bullet will have a cleaner airflw than a gg, simply because it has smooth sides.
    keep safe,

  3. #23
    Boolit Master

    Hickok's Avatar
    Join Date
    Apr 2008
    High mountains of WV
    Really great information, thanks guys!
    Maker of Silver Boolits for Werewolf hunting.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check