There was a black tipped Lapua.. but it wasn't much in the way of armor piercing. I believe it was basically a steel core round, might have been hardend vs. a mild steel core. But, the x39 is not a high pressure high velocity round so thats not helping it, you end up with the equivalent of say a .30-30 with steel core. It is kind of mundane when you compare it with other centerfire rounds with steel cores, a x54r, 8mm, or even .30-06 M2 black tip. It would rank maybe with Chinese x39 steel cored and Russian x39 steel core. Now, there is a Russian x39 round API-BZ, it has a tungsten core.
It is banned from importation,....as for legality on having it, I cant imagine when there is a crap ton of .30-06 black tip AP ammo available on the market, now, certain states it's legality may be questionable.
US Code Title 18 Section 921
(B) The term “armor piercing ammunition” means—
(i) a projectile or projectile core which may be used in a handgun and which is constructed entirely (excluding the presence of traces of other substances) from one or a combination of tungsten alloys, steel, iron, brass, bronze, beryllium copper, or depleted uranium; or
(ii) a full jacketed projectile larger than .22 caliber designed and intended for use in a handgun and whose jacket has a weight of more than 25 percent of the total weight of the projectile.
So you can legally have depleted uranium bullets in some weird caliber like .338 lapua magnum or .600Nitro Express as long as there is no handgun that also fires that round. Again....depends on state and local laws.
Ammo myths are funny.. the same aura surrounds Black Talon ammo.. 40-60 dollars or more a box.... it's still pretty much available today, just in a different box and with a different look... Winchester SXT and later, Winchester PDX1 bonded.