Rock 33, this is not advice, merely a reply. I also have a Mark II .243. When I first purchased it a few years ago, I purchased two boxes of Winchester ammo for it. One box had 80 gr pointed soft point projectiles. The second was loaded with 100 gr power point projectiles. As with an old, Remington 788 I've had for many years chambered for 6mm Remington, and the same barrel length, the two rifles tend to prefer the 100 gr projectiles. The .243 shoots one inch groups at 100 yards. The 80 gr projectiles open the group size to approx two inches. Being recently retired, I now have time to play with hand loading both cartridges. In the .243, I experimented with some 100 gr boat tail blems. They were free so I felt, what the heck? For paper punching at 100 yards, the accuracy was decidedly not what I would want to take on a hunting expedition! Those were just a fun way to punch paper. I have load data for both cartridges obtained from a magazine article years ago published in Shooting Times comparing the accuracy of both side by side. Sadly, the propellant that seemed dandy for both is no longer in production. That powder was Winchester 785, and it did make outstanding 6mm loads. I'm not sure how others reading this may feel, but for both calibers, it would appear a slower-burning, ball or flattened ball type propellant may be worth consideration. Both my rifles are scoped 3-9 with fine reticles. Lastly, I have also had good results with slow-burning propellants like IMR 4350. Good luck!