I get 200 yard groups around 1.5" with the factory loads (best has been the Hornady factory loaded 55 grain VMax). I just got my barrel late last summer and handloads were getting in the ~ 1" range at 200 yards, but haven't tried many variations yet. I know it will do better since I haven't hardly tried load variations yet.
I have the 26" heavy 223 barrel also, and it will shoot 3/4 at 200 yards. I found that the bullet weights from 50-55 have been best in it when seated out to almost touch the lands (powder was BLC-2). I don't remember my charge weight, still have my notes packed away.
As for a 243, I really don't know. I am getting a custom later this year in 26", cannot wait.
Rich C.