Abstract: This invention relates to the manufacture of composite propellants containing rubbery binders and particulate non-binder ingredients. The process consists of curing a mixture of a functionally-terminated hydro-carbon prepolymer and a cross-linking agent to form a viscoelastic first binder composition, mixing the binder with non-binder ingredients to form a plastic propellant, and rubberising at least a part of the plastic propellant by adding to it a further quantity of the cross-linking agent, provided the propellant is formed into a propellant charge while still in a plastic state. The further quantity of the cross-linking agent may be mixed in with the plastic propellant prior to forming, or applied to the surface of the plastic propellant after having been formed into a charge.In a preferred embodiment of the invention, the prepolymer consists of an hydroxy-terminated polybutadiene having a molecular weight of about 3000 and a functionally of about 2.