Thank you. Now how much does velocity play into stability. Will say 100fps make a big difference?
Very little to none.
People assign too much credit to velocity and notions of 'RPMs'..
Declared stability requirements come down -not to turns per time(RPM), but displacement per turn (with that displacement being at a standard air density). A bullet maker for example may say you need no more than 12" of displacement per turn (12:1) under StdMetro conditions. This passes tests. Where your air density is not at a 'standard' then both BC and Sg are affected by that different relative displacement(regardless of RPM's).
I calculate your Sg at 1.290(marginal) for that altitude & temp. At ICAO seal level standard, I calculate Sg at 1.145, and at your altitude but 90deg I get 1.364.
That's at 3200'/60deg/3580fps, so lets look at just what velocity does(at the muzzle);
1.117 at 2500
1.290 at 3580
1.302 at 3680
1.359 at 4500
1.440 at 5000
Notice that even while RPMs are twice as high at 5000fps compared to 2500fps, Sg barely crept up, and the bullet never reaches fully stable at the muzzle. The only reason stability rose at all with velocity amounts to the same reason BC went up,, the drag curve.
But, stability & BC are not tied either.
The bullet being marginally stable as it is for you, would seemingly tumble before transonic velocities, again because of it's drag curve, but it won't in reality. This, because by the time it slows to this velocity, turns have not slowed nearly so much. So you end up with way less displacement per turns down at that range. In fact by 200yds, your velocity will have dropped from 3580fps to 2954fps, and your relative displacement has dropped to 12.3:1, and by then
your 200yd Sg is up to 1.567 (fully stable), while G1BC dropped from .321 to .293.
See, stability at muzzle release is way different than down range. It's going up down range, even while RPMs are dropping.
Hope this helps with understandings.
.
