From: infmx!gregm@uunet.UU.NET (Greg Mitchell)
Newsgroups: rec.guns
Subject: Re: .308 for 1000 yd. Matches
Date: 23 Jul 92 14:30:35 GMT
Organization: Informix Software, Inc.

In article <9207211415.AA21075@hpfcmgw.fc.hp.com> bartb@hpfcmgw.fc.hp.com (Bart Bobbitt) writes:
#Some posts and responses regarding the use of .308 Win. or 7.62mm NATO in
#long range matches have been posted.  Their comments about bullets going
#subsonic before going through the paper at 1000 yards echo those I've heard
#on the range.
#
#One of the highpower competitors here in Colorado says his M1A does not keep
#M852 ammo supersonic at the Nationals in Camp Perry (590 ft. altitude) but
                                                      ^^^^^^^^^^^^^^^^
#the same lot of ammo is supersonic at the NRA Whittington Center in Raton
#(6600 ft. altitude); both are at 1000 yards.  At Perry, his bullets `whoosh'
  ^^^^^^^^^^^^^^^^^
#through the paper but at Raton, they `snap' as they go through.  When he
#used Lake City M118 (173-gr. M2 bullet) ammo, at both places the bullets
#`snapped' through the target.  This kind of indicates that the M2 match bullet
#has a higher BC than the Sierra 168, or, the M118 ammo has a higher muzzle
#velocity than M118 in his rifle.

I'd like to propose some conjecture ...

I really should know the answer to this, being a pilot ( haven't been
flying in a few years though ).  As the air density decreases the speed
of sound increases.  Isn't this relation linerally proportional ? 
If I had my flight computer handy I'd know for sure.

The bullet will decelerate slower in the thinner air, but shouldn't
it cross through the trans-sonic at a higher speed ?  Where in the
bullet's travel will this be ?  Decelaration is non-linear, correct ?
( I'm trying to not sound too stupid here so please give me a break ;-)
Is the fast part of the deceleration at the begining of the bullet's
flight or the end ?  If it is at the end of the flight then I can see
how the bullet would remain supersonic for a greater portion of its
usefull trajectory at higher altitudes.

One more thing.  In aerodynamic flight there is a phenomenon known as
flutter ( aeroelasticsomethingorother ).  Flutter causes violent
vibrations on the control members of an airplane.  I believe that
flutter occurs in a range of speed rather than some simple
upper limit.  The interesting thing about flutter ( besides it
ripping the wings off your airplane ) is that it occurs at true
airspeed rather than indicated airspeed.  As the air gets thinner
the airplane needs to go faster through the air ( true airspeed )
to generate the forces required to stay flying, but the airspeed
indicator ( indicated airspeed ) shows the same speeds at any
altitude because it also works by the same forces that allow 
the wings to keep the airplane in the air.  So I wonder if bullets
might experience flutter, causing their flight path to be destablized.
If they do then it might be that at higher altitudes the reduced air
friction is allowing the bullet's true airspeed to stay above the
envelope for flutter ( rather than keeping it out of the
trans-sonic envelope ) until the bullet has passed through the target.

I wonder if there isn't more to bullet destablization than crossing
through the trans-sonic. 


     Greg Mitchell               gregm@informix.com