Related Rule
Practice Relating to Rule 78. Exploding Bullets
Germany’s Military Manual (1992) states:
In the 1868 St. Petersburg Declaration the use of explosive and incendiary projectiles under 400 grammes was prohibited, since these projectiles were deemed to cause disproportionately severe injury to soldiers, which is not necessary for putting them out of action. This prohibition is only of limited importance now, since it is reduced by customary law to the use of explosive and incendiary projectiles of a weight significantly lower than 400 grammes which can disable only the individual directly concerned but not any other persons. 20 mm high-explosive grenades and projectiles of a similar calibre are not prohibited. 
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 Konflikten – Handbuch, August 1992, § 406.