Abstract: 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.