madsenshooter wrote on Nov 19^th, 2016 at 10:06pm:

. . . wouldn't it require an improved configuration to clean up the .243 chamber?,  Unless it's setback.

Yes, unless you're sufficiently unconventional to accept the ~.020" secondary shoulder that appears when we ream a .243 Win to .244 Rem. Fired brass might look a little odd, but should function fine in a neck-sizing environment.