Define "all over the place" for us. Two inches, ten inches, three feet?
I would check to make sure the bases and rings are all tight, and that the scope has not been damaged at all (does it tinkle if you shake the whole thing?). Check it all. Take it back to 25 yards and start over. Three shots there, then three shots at 100, then see what it does at 200 if that is the distance you want to use it at.
Other possibilities include mixed ammo (easy to do with a .223 and probably not so easy to do with a .243, but possible), anticipating the recoil when you fire, etc.
If you are shooting very heavy or very light bullets you may have discovered that the rifling twist is wrong for the bullets. My .243 will shoot sub-MOA with 75-100 grain bullets, and 3 foot groups with 60 grain bullets.