Wouldn't need a whole upper, just a barrel. Bolt and everything is the same. According to which barrel you get, you might need a different GB as well. But the BCG is the same for either caliber. If you are seriously thinking about a .338fed, I will send you the links to the parts I ordered up for mine relying heavily on our resident AR genius NoMercy for advise of where to get the things. My other 3 AR's I just ordered up from Accuracy Systems. Little salty but all 3 are fantastic shooters and runners. This .338 I'm getting I only have a little over 1k in. About the same as you are thinking of in that oracle. Let me gather all the links and send them to you. I'll have to look up my order sheets and such.