It was designed by Mark White of Sound Technologies, a US Class II manufacturer specializing in sound suppressors. The idea was that if you are going to use a subsonic cartridge, it might as well use the largest diameter projectile possible.

“White has developed an interesting 58 caliber subsonic PISTOL round (inspired by the .45 ACP) to push a 550 grain lead bullet of unusual design. The front of the pojectile is lightly dished with sharp edges. Back in the days of armored knights, crossbow bolts were designed with broadheads ending in a similar blunt design with sharp edges, rather than points. These specialized bolts would bite into a knight’s armor rather than glance off when impact was other than 90 degrees. Much later, when whalers began to kill whales with explosive projectiles, this blunt design with sharp edges reappeared for the same reason. Mark is awaiting approval from BATF to begin making these rounds and firearms for them…” The .58 White cartridge, with aluminum case, is pictured in the article. “Machine Gun News,” Volume 6 No. 2, July 1992, pages 25-28 (IAA Forum)

    Shorter cased version aluminium dummy