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