Four steel pipes welded or taped together in a square cluster, each serving as a barrel for a single shotgun shell. The Four Horsemen fires all four barrels in sequence by rotating a crude striker mechanism — turn, fire, turn, fire — giving the operator four shots before the weapon needs to be completely reloaded by extracting spent shells and inserting new ones. The weapon fires .410 shotshells, the smallest common shotgun ammunition, which is cheap, available, and devastating at the 3-5 meter range where the Four Horsemen is most likely to be used.

The Four Horsemen is the Shelf's answer to volume of fire. Where the Nail Biter gives you one shot, the Horsemen gives you four — enough to clear a room, defend a doorway, or ensure that a missed first shot isn't your last. The weapon is larger and heavier than a Nail Biter, carried in a coat pocket or a bag rather than concealed in a waistband, and its crude construction means accuracy degrades rapidly beyond arm's length. But at arm's length, four .410 shotshells fired in rapid succession are lethal regardless of precision.

Construction quality varies wildly. The best Four Horsemen use welded steel pipe with filed chambers and a machined striker plate. The worst use electrical tape and hope. The weapon's four-barrel design means that a malfunction in one barrel doesn't necessarily prevent the others from firing, providing a crude form of redundancy that single-barrel designs lack.