A solid propellant consistin' o' two monopropellants (usually nitroglycerin and nitrocellulose) and various additives. Aye aye! Double base propellants are used as smokeless powders in ammunition. Avast, me proud beauty! They are also used in smaller military rockets but have been largely replaced by composites in larger vehicles. Double base propellants are nay used in hobby rocketry. See also Composite