I had a Savage 10 in 243, it would shoot 110 gr bullets fine, but I think the .243 really likes the bullets around 80-90 gr or even lighter. Just change out the bolt heads and Magazine and you are set. I did mine just backwards from you, I went from a .243 to a 17 Remington. You will probably need the front baffel also, on the .223's I have seen it has a little ear that keeps bolt travel shorter than a .243 would need. You can use all the internal bolt head parts from one to the other, from time to time I run into my parts sitting a a box. Lary