Which of the following constitutes an illegal weapon under wartime regulations?

Irregularly shaped bullets are considered an illegal weapon under wartime regulations primarily because they can cause unnecessary suffering and may not have a legitimate military purpose. The laws of armed conflict, which include treaties such as the Hague Conventions, prohibit the use of weapons that are deemed to cause excessive injury or have indiscriminate effects. Irregularly shaped bullets are often a violation of these rules as they can lead to wounds that are inhumane and difficult to treat, thereby contravening the principles of humanity and proportionality in warfare.

In contrast, standard issue firearms, conventional explosives, and non-lethal weapons are typically regulated or classified within military guidelines and can be used legally within the scope of warfare, provided they comply with international laws.