Related Rule
United States of America
Practice Relating to Rule 78. Exploding Bullets
The US Air Force Pamphlet (1976) states: “International law has condemned … exploding bullets because of types of injuries and inevitability of death.” 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 6-3(b)(2).
In 1998, in a legal review of a 12.7 mm explosive bullet, the US Department of the Army stated: “A projectile that will explode on impact with the human body would be prohibited by the law of war from use for anti-personnel purposes. This remains the view of the US.” 
United States, Department of the Army, Office of the Judge Advocate General, DAJA-IO (27-1A), Subject: Mk211, MOD O, Cal. 50 Multi-purpose Projectiles: Legal Review, 19 February 1998.
In an update of this legal review in 2000, the US Department of the Army stated:
The considerable practice of nations during this century suggests that States accept that an exploding projectile designed exclusively for antipersonnel use would be prohibited, as there is no military purpose for it. 
United States, Department of the Army, Office of the Judge Advocate General, DAJA-IO (27-1A), Subject: Mk211, MOD O, Cal. 50 Multipurpose Projectile: Legal Review, 14 January 2000, p. 17.
At the Third Preparatory Committee for the Second Review Conference of States Parties to the Convention on Certain Conventional Weapons in 2001, the United States stated that it agreed with the ICRC “that there is no valid military requirement for a bullet designed to explode upon impact with the human body”. 
United States, Statement at the Third Preparatory Committee for the Second Review Conference of States Parties to the Convention on Certain Conventional Weapons, Geneva, 24–28 September 2001, UN Doc. CCW/CONF.II/PC.3/PV.1, 5 October 2001, p. 54.
In November 2006, the US Departments of State and Defense released the details of a joint letter forwarded by those departments to the ICRC President regarding US Initial Reactions to the ICRC Study on Customary International Humanitarian Law. This letter stated in part:
Although anti-personnel bullets designed specifically to explode within the human body clearly are illegal, and although weapons, including exploding bullets, may not be used to inflict unnecessary suffering, rule 78, as written, indicates a broader and less well-defined prohibition. The rule itself suffers from at least two problems. First, it fails to define which weapons are covered by the phrase “bullets which explode within the human body.” To the extent that the Study intends the rule to cover bullets that could, under some circumstances, explode in the human body (but were not designed to do so), State practice and the ICRC’s Commentary on the 1977 Additional Protocol reflect that States have not accepted that broad prohibition. Second, there are two types of exploding bullets. The first is a projectile designed to explode in the human body, which the United States agrees would be prohibited. The second is a high-explosive projectile designed primarily for anti-materiel purposes (not designed to explode in the human body), which may be employed for anti-materiel and anti-personnel purposes. Rule 78 fails to distinguish between the two. If, as the language suggests, the Study is asserting that there is a customary international law prohibition on the anti-personnel use of anti-material exploding bullets, the Study has disregarded key State practice in this area. Third, the Study extrapolates the rule to non-international conflicts without a basis for doing so. 
United States, Joint letter to the ICRC President, Dr Jakob Kellenberger, from US Department of State Legal Adviser, John B. Bellinger, and US Department of Defense General Counsel, William J. Haynes, on US Initial Reactions to the ICRC Study on Customary International Humanitarian Law, 3 November 2006.