Why do bullets and casings have casings, instead of directly punching out the exposed bullets inside? Can shell casings be recycled and reproduced? Why is there smoke and flame when shooting with a gun?
Because naked ammunition is very unsafe and reliable to use, especially gunpowder is directly exposed to the external environment, which is sensitive to weather and external forces, so it is very inconvenient to use and needs the protection of shell casings. Only a few guns do not use shells, such as the main guns of warships. Because it is too big, it is directly loaded with propellant charge, and there is no shell of propellant. Of course, this is all relative to guns and firearms under the current principles. Under some principles, the emitted energy is separated from the emitted object, so of course there are no shells after the launch, such as electromagnetic guns, electrothermal guns, liquid gunpowder guns and so on. The shell-less bullets that once appeared were finally abandoned because of immature technology, which once again showed the important protective effect of shell casings on gunpowder.
Of course, artillery shells can be recycled, especially copper shells use precious copper resources. Unless it is wartime, the usual copper coins can be recycled. The smoke and flame when firearms are fired are mainly the result of the combustion of gunpowder gas.