Usually even 168gr bullets from 308 factory loads or handloads with bullets seated to factory length in fired in 22 to 26" barrels will not always stay supersonic to 1000 yards.
Back in the day the Sierra 180gr Matchking, and the 180gr Gameking were made with a long boattail, similar to the USGI 172 Match bullet.
These bullets in loads suitable for the M14 would stay supersonic to 1000 yards.
THEN Sierra changed the boattail on their 180gr MK bullet to be the same as the 168 MK.
All of a sudden, they would not stay supersonic to 1000 yards either.
However the hunting bullets kept the long boattail and some of us used them at 1000.
For those of you that have not shot a lot at 1000 yards, when a bullet goes subsonic before it gets to 100 yards the vertical dispersion increases tremendiously, and many of the bullets hit the target sideways.
Many that shot the M14 at 1000 yards, used special set up M14's that had their barrels long throated, and shot hot loads, as at 1000 you single load only.
I used to try to get all the USGI 173gr Match ammo I could. It did not shoot as good to 600 yards as Federal Match or my 168gr MK handloads, but it shot better at 1000 yards as it ALWAYS remained supersonic.
In my Any/Any 1000 yard bolt rifle I used the old Sierra 180MK, and when they dried up I used Berger 185 VLD's.
I woud not even consider using 155 Palma bullets at 1000 unless I had a real Palma rifle with at least a 30" barrel.
The Fedeal 168gr Match ammo will make it to 1000 on some days, but the next day if weather conditions change they will hit sideways at 1000. I have had it happen many times as our Issue ammo was Federal Match, and we shot to 1000 yards on a regular basis.
Federal Match did shoot great to 800 yards on any day, but it was hit and miss at 1000, that is why after Sierra messed up the 180 MK they eventually came out with the 175gr bullet mainly for the Military for Sniper ammo.
I did have some input with the Military development of their 175gr ammo, they tried to use ball powder and had too much verticle dispersion. They were advised to switch to an extruded powder. They did not want to do so because of the ease of measuring ball powder and the expense, of the extruded powder, but when they did so the verticle dispersion went away, and the ammo was a lot more accurate.