Percussion caps (percussion primers) consist of a small container, generally metallic, usually containing a mixture based on lead trinitroresorcinate (styphnate) with the addition of tetrazene and various oxidising and reducing agents; charges of this explosive mixture usually weigh between 10 and 200 mg. These caps are intended for fixing in the bases of cartridge cases and are used to ignite propellent powder.
Friction percussion caps or firing tubes consist generally of two concentric metal or cardboard tubes containing different charges. The explosive charge in the inner tube is ignited by the tearing out of a saw-toothed wire and thus fires the charge of powder between the two tubes which transmits the ignition. Like the caps described in (1) above, firing tubes are used for firing propellent powders.