From my dark recollections, Explosives Inspector “Mac” McGaw, (Qld) once destroyed over ten thousand of these Flat tipped rounds in one sitting at the Explosives Reserve range (back in the 1960s). They had come in as scrap metal from one of the Pacific Islands Airstrips (some islands’ main economy is scrap metal collection from WW II).
Mac had been an ordnance tech during the latter years of WW II, in the Pacific, and when he switched to a public service job with the Mines Department post-war, he was “the” expert in “bringback” souvenirs from the Pacific War, American, Aussie and Japanese.
Elks, in his treatise on Japanese ammo, shows several variations of the “HE” type bullet, with the two jacket versions (common in the 12,7x81 SR cannon round) and the “percussion” version, as used in the smaller calibres (which also used the double jacket type as well. The Double jacket version replaced the more intricate Fused (Breda) HE-I used by the Japanese in 12,7 ( and 13,2mm) in the early part of the war
Later in the war, Picric Acid was used instead of RDX/PETN, and these were “bore sensitive”.
The Japanese Naval Type 87/92 7,7x56R ( aka .303) also had an explosive bullet variant…much used in New Guinea Postwar…it would punch a large hole in a Palm tree (or a neighbouring (enemy) tribesman.)
Regards, Doc AV