I think with the small bullets variables like plastic tips become much more important. When I run the numbers for the 53 gr Vmax out of a measured 14" twist 22-250, it spits out a .86 Sg and they seem to stalize just fine out of my rifle.
I'm guessing the Berger calculator might be tweaked to reflect the stability of their cup and core HP VLD bullets.
There are a lot of variables in the stability formula such as specific gravity, length and shape of boat tail if any, length and shape of nose, specific gravity of the bullet, etc., that Berger doesn't include in the inputs.
The plastic tip alters the specific gravity of the bullet and also pushes the CG back