1129 fps, exact reason?


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Alabama2010
March 27, 2010, 03:05 PM
I've been reading about F-class and Palma matches and think this is something I'd like to try starting later this year, so I've been reading up on long distance target shooting. Every source I've read talks about the bullet velocity needing to be 1129 fps at 100yds (or thereabout depending on elevation). They give the BC and MV needed to achieve that as well. But they never mention why it needs to be supersonic at 1000 yds. The only thing that comes to mind is that it must be at this velocity that the bullet begins to tumble or drop precipitously. Anyone know for sure? Is that correct? I'm sure a BTHP would still kill medium sized game if traveling at 1000 fps vs. 1129 fps- so it can't be that....
Thanks.

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Ridgerunner665
March 27, 2010, 03:31 PM
1129 fps is the average speed of sound at sea level...

Stability...thats the answer you're looking for (in a nutshell)

rcmodel
March 27, 2010, 03:50 PM
Ever watch those old movies where John Glenn was trying to break the sound barrier in a Bell X-1 rocket plane?
Remember the airplane buffeting and instability he experienced as he broke the speed of sound the first time?

If the bullet slows below the speed of sound at 900 or 950 yards, the supersonic bow shock wave goes away and forces the bullet to plow on through the air of it's own accord.
It then gets buffeted during the transition from supersonic to subsonic, and may end up slightly off course by the time it gets to the 1,000 yard target.

rc

ReloaderFred
March 27, 2010, 04:42 PM
Sorry RC, but it was Chuck Yeager who first broke the sound barrier on Oct. 14th, 1947.

John Glenn was the first American to orbit the earth.

Fred

rcmodel
March 27, 2010, 04:49 PM
:banghead:
Dang! I knew that!

I'm losing it for sure!!

rc

SharpsDressedMan
March 27, 2010, 05:02 PM
I can tell you that even bullets that yaw at the 1000 yard line can be darn accurate. The big black "dot" at 1000 yards is, I believe, about 36" in diameter, and includes the 10, 9, and 8 rings. (Anyone, correct me if my info is wrong on this, I trying to recall from a couple years ago in the pits.) Many master shots used .308's, and their bullets were yawing due to crossing the sound barrier. Still in the black, and many were 9's and 10's.

ants
March 27, 2010, 05:26 PM
Induced yaw doesn't cause the bullet to spontaneously change course (although turbulance can do that when transitioning into or out of supersonic velocity), yaw does decelerate the projectile rapidly which strings it downward on the target and makes it more susceptible to wind drift because it loses its gyroscopic stability.

I bet those master shooters mentioned by Sharps were very skilled at doping everything, not just wind and mirage but also yaw and pitch. It must have been fun to sit and watch them, Sharps.

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