Optimal Barrel Length for XCR 6.5 Grendel pistol?

[MeatAxe]

^ Good point - will need a “medium length” receiver that will accommodate both pistol and rifle-length barrels. Would probably get an additional 12” 7.62x39 barrel since they don’t lose much velocity compared to a rifle length bbl. and share the same bolt / carrier with the 6.5 G.