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Expanding or frangible small arm projectiles are prohibited for military use according the Law Of Armed Conflict or LOAC.

"C. Consideration of Specific Weapons. As noted above, HR article 22, states that the right of belligerents to adopt means of injuring the enemy is not unlimited. Furthermore, “it is especially forbidden . . . to employ arms, projectiles or material calculated to cause unnecessary suffering.” (HR art. 23(e)). The following weapons and munitions are considered under this general principle.
1. Small Arms Projectiles. Must not be exploding or expanding projectiles. The 1868 Declaration of St. Petersburg prohibits exploding rounds of less than 400 grams (14 ounces). The 1899 Hague Convention prohibits expanding rounds. Though not a party to either convention, U.S. practice accedes to these prohibitions as being customary international law. Current state practice is to use jacketed small arms ammunition, thereby reducing bullet expansion on impact.

a. Hollow point ammunition. Typically, this is semi-jacketed ammunition designed to expand dramatically upon impact. Customary international law and the treaties mentioned above prohibit use of this ammunition in armed conflict against combatants.

b. Frangible ammunition. Ammunition designed to break apart upon impact, thereby reducing ricochet. These rounds are also known to produce wounds similar to those suffered by victims of hollow-point ammunition, possibly violating the principle of unnecessary suffering. Use of this ammunition may be lawful in limited situations to significantly reduce collateral damage to noncombatants and protected property, e.g., during a hostage rescue, aircraft security mission, or urban combat to minimize penetration of walls or risk to bystanders."

http://www.loc.gov/rr/frd/Military_Law/ ... k-2012.pdf