Can shell casings be taken out of the army after soldiers leave the army?

This can clearly tell you that the regulations are absolutely not allowed. According to the regulations, shell casings should be 100% recycled.

Moreover, routine inspections should be carried out when leaving the army. If you find hidden shell casings, you should take them back. If the circumstances are serious, you may be punished.

However, in practice, it may be because of insufficient attention and difficult management that some shells are left in the hands of individuals, but I suggest you hand them in.