Within a counteracting block and tackle system of compact arrow launching devices, a cable-suspended, moveable pulley block structure permits the through clearance of razor-edged arrow broadheads and employs a plurality of low-density, solid sheaves, aligned in series to guide the in-line purchase of bowstring. The moveable pulley block has a hollow-though structure that permits the radial clearance of an arrow broadhead, reducing potential external interference or contact with the razor edges of the broadhead. The pulley block is attached to cable terminals at one end which allow the pulley block to travel in cooperating with cables. The pulley block has low-density, solid sheaves that facilitate high velocity launching cord travel with low rotational momentum for reduced friction and wear. The sheaves and cable terminals, and any launching cord terminals, are aligned in series and share a single linear plane to minimize launching cord fleet angles, reduce friction and increase efficiency.