I also ran some test loads of CFE223 through a CAR15 HBAR Elite with a 1:9 twist. I used 55gr FMJ bullets and CCI 400 primers, with an OAL of 2.250 to 2.255 inches. I did 8 different loads, started at 26.0 grains of powder and ran in 0.2 grain increments up through 27.4 grains. At 100 yards, I found that loads from 26.4 through about 26.8 grains did very well, with 26.4 being the best. In fact, the 26.4 grain loads performed almost identically to the 25.0 grain Varget load I'd used to sight my gun in on (same bullets/primers). As I increased the charge with CFE223, I found the groups were creeping lower on the target and opening up quite a bit.
I've used 26.4 grains to load a few hundred more rounds but have yet to shoot them.