According to Franklin B. Mallory, "The Krag Rifle Story", the U.S. purchased ten million rounds of .30-40 ammunition from the British firm of Kynoch, Ltd. in 1898, to meet demands of the Spanish War and subsequent actions.  It was loaded with Cordite and found unsuitable in Carbines because of incomplete combustion.  Such rounds are head-stamped "K" for Kynoch, "C" for Cordite, and '98 or '99.  Later versions of Cordite, in .303 Cartridges, had reduced nitroglycerin content and were obviously successful in 24 inch Lee-Enfield barrels.  (a photo of Cordite I dumped out of a British cartridge years ago).