Rem vssf,
After reviewing your "barrel heating" prior post etc. And apparently 5 shot by 5 group 100 yard average is really that tight "1/4 - 1/2". Even if it was just moa. It should not go to 6" @ 300 yards.
Your cooling and cleaning practices are sound, wind is not the issue apparently. 50 grain b-tips shoot very well in 22-250's including 300 yards as a whole. Re-loads or factory ? You have a rear bunny ear bag correct ?
Parellax adjusted at 300 ?
I would suggest cleaning well for copper. Then buy a couple boxes of Hornady 50 grain V Max factory ammo from the same lot and head to the range again, shoot two foulers, start at 300 and not 100 yards. Black diamond targets as noted. You may need them a little larger for that scope power depending on it's contrast quality.
