What’s the purpose of this? Is it a Saint Louis special?
There was a .30 cal. Triplex experimental made, using Three M1 Carbine Bullets…The Duplex version is more common…but this one may be a “Dingbat”: ( fantasy fake).
It looks very similar to a cartridge that the late Ray Meketa posted a picture of here on this forum several years ago he called the .30 Giraffe.