That depends on whether the brake is permanently attached or can be removed without major effort.
In other words, if the brake can be removed by unscrewing, driving out a pin, or removing a lock screw, the brake DOES NOT count for barrel length, and the barrel MUST be at least 16" long without the brake.
If the brake is welded, BRAZED (NOT soft soldered) or blind pinned so it can't be easily removed, it does figure in the total length, and the barrel PLUS brake must be 16".