458 1 1/2" barnes

hello again am wondering if anyone has any imfo on the barnes 458 1 1/2" military round experimemted with in vietman. according to barnes the u.s. destroyed all the ammo in the 1980’s. who made the ammo for the u.s.? what was the headstamp? it was supposed to be a 500 grn. fmj solid from? hornaday? does anyone have any photos of the original round? any imfo would be a help.

There is a picture of the rifle in one of Peter Senich’s books. I can see why it was unpopular. The suppressor was ridiculously huge.