Late to the party here, but in my experience inaccurate 243’s is usually due to the bullets rather than the other components. Lighter bullets have done the trick for me. 75 to 85 grains seems to be the sweet spot. All my experience with this caliber has been with Handi Rifles. Don’t know if that makes a difference or not.I've got an interesting one right now. My brother called and asked if I could do .243 - which I can. He said he's tried all the commercial ammo he can get, but nothing groups, so could L see what I can do. He dropped the rifle off - a Model 70 - and I checked the mounts and made sure the gun was clean. (I knew it was a waste of time as he takes good care of his guns, but you start with the basics) Now I'm going through the componants I have wondering where to start. So, realizing every gun is different, who has experience with this caliber? I'm thinking start with RL22 and W760 - maybe 3031 - and 100 grain Sierra boat tails. Federal match primers, maybe magnums in the 760. I have Hornady and Winchester brass. Size and trim and clean primer pockets to eliminate as many variables as possible. Any sugggestions for powder would helpful.