Browning .50 caliber machine gun
True machine guns fire rifle cartridges and must have a locking system to secure the breech against pressures approaching 65,000 psi. The extra time required for locking and unlocking a machine gun often causes a somewhat slower cyclic rate of fire. Machine guns may be fed from spring-loaded box magazines, gravity feed magazines, or belts.
The most noteworthy firearms design and ammunition development occurred from the 1700s through the 1900s. Modern firearms operating systems are evolutionary products resulting from concepts developed in the late 1800s and early 1900s. Materials and manufacturing precision have improved; cartridges are more powerful and compact. The essence of good early designs remains the basis of every modern firearm.