With the 1:8 twist I would look at a longer (higher BC bullet) its amazing how the bit slower but higher BC bullet carries the energy much further out in the 243. Berger has some high BC options, the 90 grain TGK from Sierra is .490, the ELD-X from Hornady is over .450 as well. Unfortunate that the loading data is for an 85 TSX or a 105 grain Match Burner in their manuals.....Would look at RL-17, Superformance, Magnum (46-50 grains), RL-25 (43-47 grains) I load for many calibers but just starting with the 243.