Are you cutting the opposite from a facegrain bowl? For endgrain rim to bottom for OD, center to rim for OD. While dry wood is harder to cut, endgrain is even more difficult if cutting the wrong direction. Long wing bowl gouges can core an endgrain bowl pretty quickly, but be careful of getting the entire wing edge into the wood - push the handle away from you as you pass through the transition curve to limit the amount of edge cutting wood. Spindle gouges are great until you get too far off the tool rest.
I use chucks, and 3/8” length for a bowl that size is plenty. Im guessing that is ~8” dia, I would use ~ 3” or slightly larger dia tenon. You can decrease tenon dia and lengthen the tenon if desired.