Related Rule
Germany
Practice Relating to Rule 77. Expanding Bullets
Germany’s Soldiers’ Manual (1991) provides: “It is prohibited to use means or methods of warfare which are intended or of a nature to cause superfluous injuries or unnecessary suffering (e.g. dum-dum bullets).” 
Germany, Taschenkarte, Humanitäres Völkerrecht in bewaffneten Konflikten – Grundsätze, Bearbeitet nach ZDv 15/2, Humanitäres Völkerrecht in bewaffneten Konflikten – Handbuch, Zentrum Innere Führung, June 1991, p. 5.
Germany’s Military Manual (1992) states:
It is prohibited to use bullets which expand or flatten easily in the human body (e.g. dum-dum bullets) … This applies also to the use of shotguns, since shot causes similar suffering unjustified from the military point of view. It is also prohibited to use projectiles of a nature:
–to burst or deform while penetrating the human body;
–to tumble early in the human body; or
–to cause shock waves leading to extensive tissue damage or even a lethal shock. 
Germany, Humanitarian Law in Armed Conflicts – Manual, DSK VV207320067, edited by The Federal Ministry of Defence of the Federal Republic of Germany, VR II 3, August 1992, English translation of ZDv 15/2, Humanitäres Völkerrecht in bewaffneten KonfliktenHandbuch, August 1992, § 407.
[emphasis in original]
Germany’s IHL Manual (1996) states: “International humanitarian law prohibits the use of a number of means of warfare which are of a nature to violate the principle of humanity and to cause unnecessary suffering, e.g. bullets which easily expand or flatten in the human body, so-called dum-dum bullets.” 
Germany, ZDv 15/1, Humanitäres Völkerrecht in bewaffneten Konflikten – Grundsätze, DSK VV230120023, Bundesministerium der Verteidigung, June 1996, § 305.
Germany’s Soldiers’ Manual (2006) states: “It is prohibited to use means or methods which are intended or of a nature, … to cause superfluous injury or unnecessary suffering (e.g. dum-dum bullets), …”. 
Germany, Druckschrift Einsatz Nr. 03, Humanitäres Völkerrecht in bewaffneten Konflikten Grundsätze, Erarbeitet nach ZDv 15/2, Humanitäres Völkerrecht in bewaffneten Konflikten Handbuch, DSK SF009320187, Bundesministerium der Verteidigung, R II 3, August 2006, p. 5.
Germany’s Law Introducing the International Crimes Code (2002) punishes anyone who, in connection with an international or non-international armed conflict, “employs bullets which expand or flatten easily in the human body, in particular bullets with a hard envelope which does not entirely cover the core or is pierced with incisions”. 
Germany, Law Introducing the International Crimes Code, 2002, Article 1, § 12(1)(3).