A rotor blade for a gas turbine that includes an airfoil and a tip shroud. The tip shroud may have a seal rail that projects radially from an outboard surface and extends circumferentially. The tip shroud may further include: a rotationally leading circumferential face; a rotationally trailing circumferential face; and an outboard face of the seal rail. The tip shroud may be circumferentially divided into three parallel reference zones: a rotationally leading edge zone, a rotationally trailing edge zone and, formed between and separating those, a middle zone. The seal rail may include a hollow cavity wholly contained within at least one of the rotationally leading edge zone and the rotationally trailing edge zone. The cavity may include a mouth formed through at least one of the rotationally leading circumferential face, the rotationally trailing circumferential face, and the outboard face of the seal rail.