I have a 6.8 SPC mini 10" barrel that I SBR'd before pistol braces were a thing. I like 6.8 /.300 in my XCR so there is no ammo crossover in my 5.56 AR's. Great rifle! I found 6.8 does not suppress that well sound wise (even tried hand loads) so I bought a .300 Blkt kit for when I want to run a can.