I've played with Trail Boss and the .223. Here's some speeds:
Ruger American Predator .223 1-8 twist
40gr Nosler BT, CCI 41 primer, Federal cases
5.5gr TB - 1670fps
5.0gr TB - 1565fps
4.5gr TB - 1434fps
4.0gr TB - 1294fps
Accuracy averaged around 1 1/2 - 2 inches @ 100 for 5 shots.
FWIW - 27.0gr of Ramshot Exterminator with 40gr BT - 3700fps & .53" group for 5 shots
