I have a 25mm French case that was reportedly modified by DuPont in the early 1930's for a test program. I have not been able to find out anything on it. There is a hole drilled in the extractor groove, but it only goes about 1/8 inch deep. The hole in the base penetrates into the inside chamber and it is lined with a copper sleeve. The case is brass. I have placed a 1934 dated 25mm round next to it for comparison. Anyone have any information on what DuPont was doing or if the story is even true?