This reminds me of the fact that, as far as I know, the USA had NOT accepted the Geneva Conventions over war, before and during WW II, and could do as they wished, for ex. use explosive ammunition below the otherwise "legal" caliber of 20 mm. I discussed exactly this point with Adolf Galland about his knee wound during his last fight on a 262. He got some shrapnell into his knee, from a .50 caliber shell it seems. I'm not quite sure, you often get shrapnell from non-explosive missiles.

Tony Wood! Help! Did the USA use explosive .50 ammunition during WW II? Was it common practice and were they normally mixed into machine-gun belts?