[time-nuts] Why .30 cal holes can't be seen at 800 yds...

Michael Baker mpb45 at clanbaker.org
Wed Nov 3 18:10:25 UTC 2010


   Timenutters--
   The question was asked-- Why can't a large aperture
   high-resolution optic be used to locate bullet holes
   in a target at 800 yards?
   Consider this--: I often shoot at targets on the
   600 yard berm at the Manatee Range (near Bradenton,
   FL).  Typically, by 11AM the atmospheric shimmering
   mirage distortion makes even the 4" target hard to see.
   By 1PM the use of any rifle scope magnification
   greater than around 10X is an exercise in futility.
   Often, the mirage is severe enough that even the
   12" steel plates are hard to find through a 10X
   scope.
   .30" holes in a target...?  No way.
   -----------------
   Other questions that were asked:  To what degree of
   accuracy can the 800 yard distance be measured?
   I have a laser range-finder which has been verified
   to be within +/- 20 inches out to 1000 yards (the
   U of F college of Engineering has a series of distance
   marker posts set up for some research they were doing).
   What kind of accuracy is expected for measuring bullet
   velocity at the shooting bench and downrange?  I have
   a set of Oehler Research sky-screen chronographs that
   use a 10MHz crystal for clocking the counting registers.
   The projectiles start out at roughly between 2750 FPS and
   3100 fps and end up downrange not slower than around
   1800 fps.  Assume sky-screen clocking ambiguities of
   only a couple of clock pulses.
   As an aside, projectiles whose velocity drops to
   sub-sonic at 800 yds are of no interest to me.
   The transition from super-sonic to sub-sonic generally
   includes conditions that create inaccuracy.
   I am VERY grateful for the feedback on this topic!
   A couple of innovative suggestions from list members
   have given me food for thought and I am going
   to pursue looking into them.
   My first chore is to investigate what kind of pulse
   rise-times I get from a selection of inexpensive
   ultrasonic sensors when a supersonic bullet passes
   within a couple of feet from them.  I have a Tek
   2252 scope that I can place downrange to look at the
   sensors with but storing the waveform for examination
   may be a problem (no one seems to have volunteered to
   stand downrange monitoring the scope screen!)
   The Tek 2252 has a Centronix screen-capture printer
   output but it is  an Epson FX format and I have no
   idea if any current printers at the local Office Mart
   are compatible with the Epson FX data format.  Anyone
   on the TimeNuts list have any thoughts on this?
   The 2252 scope also has a GPIB port but I don't know
   if it outputs the printer data.  I have a Sparkfun
   GPIB/USB dongle but that may not be of any use if
   there is no printer data on the GPIB port.
   Mike Baker
   -------------------



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