Hague convention on bullets:
http://avalon.law.yale.edu/19th_century/dec99-03.asp"The Contracting Parties agree to abstain from the use of bullets which expand or flatten easily in the human body, such as bullets with a hard envelope which does not entirely cover the core, or is pierced with incisions.
The present Declaration is only binding for the Contracting Powers in the case of a war between two or more of them.
It shall cease to be binding from the time when, in a war between the Contracting Parties, one of the belligerents is joined by a non-Contracting Power. "
