So that is a technical question. Although I am not a professional tuner but I do tuning for pleasure.
Accuracy is a combination of projectile, barrel, rpm of the projectile and fps.
Now if we keep the projectile and barrel constant, the rest of accuracy depends on fps and effective rpm.
Effective rpm are different from twist rate of barrel.
When a projectile is shot from a barrel, we need to achieve the best combination of fps and rpm of the projectile for extreme accuracy.
The actual phenomenon is the as the projectile moves forward, the rpm do not reduces as rapidly as the fps is reduced.
In order to keep the best combination of fps and rpm of the projectile, we need to maintain the best combination between the both.
If the accuracy is fine at 50 yards it means that rpm and fps combination is fine for that distance. But if you stretch to 100 yards, the rpm does not get slow down with same ratio as the fps slows down. This disturbs the effective combination of rpm and fps as well as accuracy.
That is why in order to achieve the best possible accuracy at any distance, the rpm and fps needs to be maintained for that distance.
One adjustment to achieve this combination is HST.
Bhaur