In theory it depends on the amount of throat erosion in the rifle.
Shorter rounds work well in a new throat, longer rounds work well in a slightly eroded throat, the longest rounds in a more eroded throat etc.
The idea is to maximize the benefit of the most efficient distance from the bullet ogive to the beginning of the lands and grooves by using the appropriate overall cartridge length.
When groups become larger use longer rounds.
I have not catalogued the variation in POI for each different length due to the military slop design of the chamber and bore and the fact that my throat has not yet eroded sufficiently to maximize the benefit of longer cartridges. The variation in point of impact was minor but will increase with increased throat erosion.
I have noticed however, that from the beginning, the longer cartridges tended to group slightly tighter {in my CZ}.
With mil-slop rifle to rifle variation, a different rifle may prefer shorter or midlength rounds.
Sorting basically minimizes the fliers that open up group size. There are still fliers because of powder volume variations and differing bullet weights but fewer of them, and closer to the main group.
For me sorted mil-surp ammo averages 1 to 1 1/2 M.O.A.
Sorted non corrosive Wolf Military Classic 124 gr. has been giving me 1/4 to 1/2 M.O.A. with many one hole groups. (very difficult to do because of the CZ trigger)
