I've loaded from 25.5 - 26.5gr W748 @ 2.230" with the 55gr Dogtowns. Out of a 16" 1:9 twist AR, velocities were 2800 - 2930 fps.
As Doubletap said above, 26.0gr worked best, but I got a little better accuracy with 26.5gr BLC-2.. worked for me.
Other good powders were AA2230 & TAC. Max charge of AA2230 pushed them along at 3107 fps. I didn't work AA2230 up for accuracy though, so i can't comment on how accurate that load was.