WRA did not load the XM256 cartridges. As Phil said, it's a completely different cartridge.
I noticed the deep seated bullet but it didn't fit with any cartridge that I knew. You may be correct about it being a fake XM256. For some reason, if you show a colored tip cartridge on the auction sites you'll get a lot of bids. Non collectors love them. And many of them are fake.
Have you checked the bullet with a magnet? It almost looks like a 7 ogive. If no one else can come up with an explanation you may have to pull it.
Ask Bill Woodin. I understand that he now has one of every cartridge ever made and maybe he can ID it.