A launcher system comprising: a projectile including: a main body having at least one vent hole, and a charge provided in the main body; and a launcher including: a barrel adapted to receive the projectile; a mechanism for activating the projectile; and a velocity variator configured to shift relative to the barrel to selectively vary a launch velocity of the projectile from the launcher, wherein said velocity variator includes a breech (34, 520) and is constituted by either: a collar formed with a passageway being mounted on the barrel whereby, when the mechanism activates the projectile and the charge is initiated, gas is created, which exits the main body through the at least one vent hole to provide thrust for the projectile, and the collar is selectively movable from a non-venting position blocking the gas from exiting a vent hole in the barrel to a venting position allowing the gas to pass from the barrel through the vent hole in the barrel into the passageway and to atmosphere whereby movement of the collar controls the launch velocity of the projectile and wherein the breech is sealed; or at least in part, by a portion of the breech which is configured to slide relative to the barrel when the launcher is fired to vary the launch velocity of the projectile from the launcher. a projectile including: a main body having at least one vent hole, and a charge provided in the main body; and a main body having at least one vent hole, and a charge provided in the main body; and a launcher including: a barrel adapted to receive the projectile; a mechanism for activating the projectile; and a velocity variator configured to shift relative to the barrel to selectively vary a launch velocity of the projectile from the launcher, wherein said velocity variator includes a breech (34, 520) and is constituted by either: a collar formed with a passageway being mounted on the barrel whereby, when the mechanism activates the projectile and the charge is initiated, gas is created, which exits the main body through the at least one vent hole to provide thrust for the projectile, and the collar is selectively movable from a non-venting position blocking the gas from exiting a vent hole in the barrel to a venting position allowing the gas to pass from the barrel through the vent hole in the barrel into the passageway and to atmosphere whereby movement of the collar controls the launch velocity of the projectile and wherein the breech is sealed; or at least in part, by a portion of the breech which is configured to slide relative to the barrel when the launcher is fired to vary the launch velocity of the projectile from the launcher. a barrel adapted to receive the projectile; a mechanism for activating the projectile; and a velocity variator configured to shift relative to the barrel to selectively vary a launch velocity of the projectile from the launcher, wherein said velocity variator includes a breech (34, 520) and is constituted by either: a collar formed with a passageway being mounted on the barrel whereby, when the mechanism activates the projectile and the charge is initiated, gas is created, which exits the main body through the at least one vent hole to provide thrust for the projectile, and the collar is selectively movable from a non-venting position blocking the gas from exiting a vent hole in the barrel to a venting position allowing the gas to pass from the barrel through the vent hole in the barrel into the passageway and to atmosphere whereby movement of the collar controls the launch velocity of the projectile and wherein the breech is sealed; or at least in part, by a portion of the breech which is configured to slide relative to the barrel when the launcher is fired to vary the launch velocity of the projectile from the launcher. a collar formed with a passageway being mounted on the barrel whereby, when the mechanism activates the projectile and the charge is initiated, gas is created, which exits the main body through the at least one vent hole to provide thrust for the projectile, and the collar is selectively movable from a non-venting position blocking the gas from exiting a vent hole in the barrel to a venting position allowing the gas to pass from the barrel through the vent hole in the barrel into the passageway and to atmosphere whereby movement of the collar controls the launch velocity of the projectile and wherein the breech is sealed; or at least in part, by a portion of the breech which is configured to slide relative to the barrel when the launcher is fired to vary the launch velocity of the projectile from the launcher.