My take, based on my limited knowledge of the various sciences, is that they should be at the most stable they are going to be upon leaving the muzzle (at their highest speed). I would think that any spinning projectile, moving forward, would only tend to become less stable as it decelerates. I will await someone more knowledgable than myself to see if my pseudo-educated guess is correct.
The stability factor actually does increase at range. The angular velocity of the projectile decreases more slowly than the linear velocity, so the aerodynamic forces on the bullet decrease faster than the gyroscopic stabilization.
Read up on bullet coning motion. Supposed to be its greatest at the muzzle. Settles out down range. Several good research articles on it, even Sierra admits it’s possible.
And there you have it, just that for which I was waiting. You (I) learn something new every day. Very interesting.