The cap was fixed on the contact hole on the gun (extended to kind a "nipple") and ignited via the effects on the gun's "hammer". (The hammer is around similar to the cock discovered on flintlocks besides that it does not clamp onto anything at all.) In the situation of https://ar-15-rifles90819.amoblog.com/an-unbiased-view-of-sig-saeur-handguns-38343821