The original Dissipator was a standard M-16 with a 20" barrel cut down to 16". They had problems with reliability. So to alleviate the issues the reliable Dissipator uppers I've used have a 16" barrel with a low-pro mid length gas block under the hand guard, with a FSB pinned at the rifle length location for a longer sight radius. What you are describing with a free float hand guard by definition would not be a Dissipator. IMO