The compact top reservoir measures 4.25 inches; it will reduce the length of pull (L.O.P.) to 13.5 inches on the standard Leshiy 2 with the original regulator; with the new R.E.P.R. regulator, it will keep the L.O.P. to 14.5 inches. This reservoir can be used to make an ultra-compact Leshy 2 when used with the original regulator. NOTE: If utilized with the original regulator, the bottom O.E.M. tube cannot be utilized, the compact 300CC bottle will fit perfectly (see photo)