a firing pin block for a firearm of the type having a rotary breech bolt , a reciprocating bolt carrier , complementary locking lugs formed on the bolt and barrel to releasably secure them together , and cam means drivingly connecting the bolt and bolt carrier for opening and closing the bolt . the firing pin block positively prevents discharge of the firearm at any time when the bolt is unlocked . it does not rely on the presence or good condition of any separate parts , but instead coordinates the cam - actuated rotary operation of the locking lugs with relative longitudinal displacements between the bolt and bolt carrier , to cause the latter to block an enlarged abutment formed on the firing pin whenever the bolt is unlocked .