An obturator ring (4) for a mortar round (2) is proposed where the geometry of the ring (4) is modified by its sliding and striking stationary anvil (18) when the round (2) is placed in the muzzle-loaded mortar's barrel (6) and reaches its bottom. The initial ring (4) geometry does not impede round's travel down the barrel (6) while its modified geometry provides a gas seal between the round (2) and the barrel (6) wall.Several embodiments featuring free-rotating (4), splined non-rotational (4a) and stationary separated (12a-14a) designs are presented.The ring works with both smoothbore and rifled mortar barrels and in several embodiments imparts rotation to the round (2) if used in a rifled barrel (6).An optimized muzzle-loaded mortar barrel (6) operating in cooperation with rounds equipped with the obturator ring of instant invention is also presented, containing rifled (6a) and smoothbore (6b) sections.