There are many on this board that have forgotten more about RB's than I will ever know, BUT; I have not seen any mention of "double action" in either Mr. Layman's books on military RB or in Mr. Marcot's new book on RB sporters. I would thing that if such a creature existed they would have been included. Perhaps someone in the know will come along with an answer. Seeing how "double action" would work on a rolling block would be verrrrry interesting.
Meanwhile consider information to be taken with a serious dose of salt I would think.
CL