I have campaigned for over 20 years in 243 with that RCBS 6mm-95-SP that Bud mentioned and the Lyman #245496. I have a third design inbound from a member here to mess around with as well. The 243 has been the best small rifle castings caliber I have tried by a wide margin over the 22s, 25s, and 6.5mms.
Good ta know. I hopefully have acquired that RCBS mold.My Ruger #1B in 6mm Remington likes the RCBS 243-095-SP and SAECO #243 (This mold casts heavy at 93 grains with Linotype alloy) sized .244 and LBT lube. My .243 Model 70 Varmint likes the same bullets.