Those shells were produced during the Cultural Revolution. During the Cultural Revolution, after Lin Biao's death, the Gang of Four launched a "criticizing forests and criticizing holes" campaign against Zhou Enlai, Deng Xiaoping and others, that is, they studied and criticized politics all day long. At that time, factory workers also studied and struggled all day long, and no one paid attention to production at all, and the products produced were full of problems. Many military products produced during this period were problematic. For example, the J -6 fighters produced in this period had serious quality problems, and many of them were returned to the factory.

The criticism of forests and holes mentioned by the company commander Liang Sanxi was actually harmful to people during the Cultural Revolution.

For details, please read this article, which is much more detailed and beautiful than movies.