Totally agree with Headquarterz.
Talk to Zach at Atheris Arms...I was looking for a 6.5 Grendle…..he talked me into the 6mm Grendel/6mm AR, I used the advice from the good folks on this site and talked to Robert Whitles (sp) son.
The dies are a bit expensive (I am assuming you reload)….but the range of bullet styles and weights available are many times that of the 6.5. Ballistics are almost equal to the .243.