CF I cut myself four bullet moulds same bullet different lengths. Originaly the goal was to see how long I could go before becoming unstable of which I did determine. Having shot all four lengths I started to notice a differance in regards to small changes in accuracy so I went off on this tangent to find out what length would turn out to be the overall best for my rifle. Over the years I have tried several bullet designs to numerous to mention to find that best design. But I have never taken that best found and played with the length to try and improve it yet further. I never even gave it any thought until I stumbled onto what I am now experiencing and it was really just by accident but it has really caught my attention. In the past I just figured if a bullet stabalized and or fit the requirements of the Miller Rule it should be good bullet. It was not until I pursued looking into how a 90 thousandths differance in bullet length would still fall under the Miller stabilization requirements. I would have never thought that there was that much leeway until I checked it for myself. I still have a multitude of targets yet to shoot with each before I can even begin to draw any honest conclusions but I thought I would share it if others would like to purue the same as the noticable differance is indeed there but to what degree still has to be determined. Its pretty common knowledge a bullet can fly with a nose up and or down attitude and still be stable but creating more drag so maybe a slight differance in length will get it to per-say fly perfectly, decrease the time of flight and up the accuracy.

I hope this made some type of sense to you CF.
JLouis

General guidelines are the Gyroscopic Stability (Sg) is just spinning fast enough at 1.4 and at 2.0 the bullet is over spinning and may affect accuracy (or for that twist a longer bullet would be more suitable).

I have had excellent results with rifles shooting with a Sg of 1.85 to 2.0 and suspect you will have no problem with a Sg of 1.9. 
However bullet nose shape does come into play specifically as you shoot longer distances.

However the stability can also be affected by temperature, barometric pressure and elevation; so you do not want to be too close to a Sg of 1.4. 

However many long range (1000 yard) shooters are pushing bullets over 2.0 (overspinning them) to allow for the drag on the bullet over longer distances.

Accuracy is initially dependent on the gyroscopic stability.
However over longer distances accuracy starts to be affected by the dynamic stability of the bullet. (i.e. drag effects based on bullet shape; nose deflection and center of gravity length wise).

Thanks guys. I have just been playing with these things- pretending that I'm learning how to use a computer, ballistics and such. 
For what it's worth the numbers I fed it were for the Ideal 319289 bullet in a sixteen twist barrel. Something that's worked for a long time and I have no intention of altering. It was just for fun, ya know. 

No, 1:20

John boy,
It is .375 groove diameter, it is a .38-50 RH and it is from a Brooks mould. Barrel is a 8 land 8 groove Douglas