The shell of the shell is made of shell steel and contains a lot of sulfur. This material is particularly brittle and has low ductility and low stress resistance. In this way, after the projectile explodes, the projectile will be broken into small pieces, which are not only small but also uniform in size, so that the maximum area and density can be achieved.

Compared with aluminum, copper and steel, aluminum is the worst, followed by copper, and steel is the best.

Because in terms of brittleness and stress resistance, this is the order.

Besides brittleness, there are other factors that affect the choice of materials.

There is a big problem with aluminum, that is, there will be a layer of alumina on the surface, which is a very, very hard substance-"corundum" is alumina. If aluminum is used as the shell, many deep slender marks will be worn on the inner wall of the barrel at one shot, which is as high as 0.3 mm during the test. This is too serious. A barrel of aluminum bullets will be scrapped after several rounds, so it is resolutely ruled out.

Copper is too expensive as the shell of artillery shells, and it will not be chosen if it is only based on cost.