Abstract: in this paper a sectional ring parametricelement model of barrel and cartridge is constructedin accordance with the characteristics of varyingclearance and taper between the cartridge and barrel of the automatic weapon, and an incrementalelasto-plastic finite element equation is established.In light of the characteristics at different momentsnestling up against the chamber, matching-pointsare allotted between the barrel and the cartridge.With aid of deformation coordinate conditions, thefinite element progr...