GG writes: [ QUOTE ]
It seems that there are several reputable sites that give conflicting info on this subject. I believe that it is all theory and no one has actually devised a way to "capture" a bullet at long range on slow mo video to see if it is still spinning the same rpd's as it was when it left the muzzle!
I found this:
Scroll down to where it says, "some caveats"
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My background is MS in applied math specializing in numerical solution of PDEs. I used this in CFD (computational fluid dynamics) as an applied mathematician at Boeing. I can't say I'm an expert on supersonic calculations as all the work I did was commercial airliner (sub-sonic). I could check with my pdh pals who do super-sonic/boundy layeer/turblent flow work, but I don't see where there is any difference in opinion. The ref you site looks very accurate to me
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Now consider a bullet chronographed at about 3000 f/s muzzle velocity fired from a rifle with say a 10" twist. It is rotating at around 3600 revolutions per second (216,000 rpm). Let the flight velocity decay to 2000 f/s. Now what is the bullet rotational speed? It doesn't fall off much because the only things slowing it down are inertia and skin friction drag which is pretty low, so the rotational velocity is only slightly slower than 3600 rps
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The statement could be made more precise.
For axial symmetric projectiles with angular laminar flow (smooth bullets), the ratio of rotational drag to translational drag is > 10^n ( I don't know, maybe 100,000) in the supersonic range.
Even with pulled bullets with surface marks (that have fairly high turbulent skin friction, the ratio is still very high)
If you provide references to conflicting sites I would be happy to review them.