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

Bob Camp lists at rtty.us
Wed Nov 3 22:11:31 UTC 2010


Hi

Roughly speaking, you know the distance to 0.1%. If the electronics are good to 0.01% they aren't going to contribute a significant amount of error. A fairly modest bare crystal will do quite nicely for the time base. No need to go any further. If you want to go time-nutty, put in a cell phone TCXO at both ends.  That will easily get you sub 0.001%. In all cases a simple adjustment to "net" them together would be required every so often (yearly ...). 

The only real issue left is how to sync the counter at the far end to the "start time". The RF link sounds like a good candidate for the job.

Bob


On Nov 3, 2010, at 2:10 PM, Michael Baker wrote:

>   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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