I have found a book on explosive bullets in France’s National Library. It is titled Balles dum-dum, balles explosibles, balles explosibles autrichiennes 1914-1916, par le Docteur Émile Dutertre-Deléiéleuse, Paris, 1916, and is available in pdf format at ftp://ftp.bnf.fr/573/N5738630_PDF_1_-1DM.pdf
The book says that the accusations of french troops using dum-dum bullets against their enemies is false, because the solid Lebel bullet cannot be converted into a dum-dum. If some expansive bullets were found in the hands of french soldiers, they were belgian.
The jacketed bullets of german, austrian and russian origin, produce greater wounds because of the dissemination of fragments. The british trimetallic bullets, with lead and aluminum core, produce similar effects. But all these bullets may cause the gravest effects if individually modified. Austria, a german ally, is the only country barbaric enough to use actual explosive bullets.
The study of an austrian explosive bullet from the austrian sector in Serbia shows an ogival bullet with a steel jacket and an inner cylinder full of mercury fulminate. At the base of the bullet an inertia striker made of copper can be found.
The explosive cartridge was identified by a black band on the case. The case was copper and at the base it read “19-14” and “C R” intertwined (GR for G. Roth, surely).
According to this book, the austrian soldiers made prisoners during the austrian-serbian war carried a number of chargers with five explosive cartridges each, making a total of twenty to twenty five rounds for each soldier.
These cartridges should be of the spotting kind, and for use in machine guns, not issued to troopers. But it is documented the existence of these explosive cartridges identified by a black band on the case, or was it just french propaganda?