3. Find the central idea
The term "machine gun" is commonly applied to any gun that is designed to fire repeatedly and in rapid succession for as long as the trigger is held down. During the course of warfare, the trigger of some machine guns may be held down almost continuously for hours to create suppressant fire (rounds fired not necessarily to kill an enemy, but to prevent them from attacking). All of this firing can generate a lot of heat, which may cause the weapon to overheat and malfunction. But this situation has been addressed in a number of ways. For one, practically all machine guns fire from an open bolt, which allows air to cool the breach between bursts of fire. Additionally, some machine guns have removable barrels, which allow hot barrels to be replaced. And some advanced machine guns even have sophisticated barrel cooling systems, which maintain a functional heat level within the weapon. As you might have concluded, a lot of brain power has gone into keeping those guns firing.
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