I owned a 308 BB but was unable to fit it up to the frame I wanted, so I have yet to actually shoot this one in a Handi. But my advice, for what it's worth, and what I have been followed, is to load them long as with many Handi's the throat is long. This one for the most part is no exception.
But a few members around here have found the right combination for theirs and I am sure will chime in soon..
-Aaron