Abstract: A hinge device for break-open type firearm comprises two pair of arcuate ridges on the breech slidably received in complementary grooves formed in parallel sidewalls of a receiver. One pair of ridges and complementary grooves is located forwardly of the hinge axis, with one ridge and its associated groove on each side of the ridge, and the other pair of the ridges and complementary grooves is located rearwardly of the hinge axis. In the closed position of the firearm, the ridges and grooves are generally upright, so that their flanks or sidewalls include a large angle with the line of action of the recoil forces.