Co-layered propellant charge

A propellant grain having an exposed outer surface, wherein said propellant grain comprises an outer layer comprising a slow burning propellant composition located on essentially the entire outer surface of the grain, and an inner layer comprising a fast burning propellant composition having a higher linear burn rate than said slow burning propellant composition, wherein said propellant grain has a structure such that after ignition, the inner layer becomes increasingly exposed at the outer surface, wherein the grain further comprises an exposed inner surface having an area that increases after ignition, wherein said propellant grain has a longitudinally extending shape and one or more perforations passing through the grain in the length direction that provide said inner surface of the grain, and wherein said inner layer is located on at least part of the inner surface.