The invention provides a self-aligning device for aiding the engagement of a munition into a rifled gun barrel on loading of the munition, absent the use of a driving band, as, for example, in the case of a munition which is fitted with aerodynamic tail fins. The device comprises at least one annular ring to surround the munition, and which, if desired, can be seated on a surface of the munition which allows the ring(s) to rotate. One or more of the rings has a number of elements which are capable of lying within the outline of the ring or rings to allow the munition to be readily loaded into a gun barrel but which can take the form of projections extending radially outwards from the ring(s) when they become coincident with the internal rifling of the gun barrel on further movement of the munition along with barrel or when the munition is rotated. The projections then engage in the rifling grooves and provide a sealing effect. Advantageously, one or more rings is/are designed to override one of the other rings when pressure is applied to the device on gun firing so as to cause the device to engage more tightly with the inner surface of the gun barrel and so providing an obturating effect.