Only reason copper alloys (brass, bronze, etc.) are considered "AP" by law is because they have superior penetration characteristics....when compared to cast lead, or copper jacketed lead bullets, not because they're actually capable of punching through 30 layers of Dyneema or X amount of Armor Steel at a particular weight/velocity. 
The whole guffaw about "teflon coated cop killers!" came about when some police officers were unhappy with the penetration characteristics of their standard issue cast lead .38 Special loads and started looking for something that would do better against vehicle glass and such. They found a .38 bronze solid did quite well, but was a bit harsh on the rifling in their pistols, hence the teflon lubrication. This spun out of control with the gun-grabbers and morphed into pistol AP ammo ban "for the children police officers!"
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Solid copper/brass isn't considered AP. IIRC, to be considered AP it has to have harder materials than lead, copper, or brass. Otherwise, all the really good VLD turned bullets would be illegal, and since you can get them in 5.56 and 7.62 legally, new, while due to the pistol restriction AP in those calibers is illegal, turned solids aren't AP.
There must also be a content aspect, because SS109 isn't illegal, and it has steel in it.
Hell, they market 55gr FMJ in 5.7x28 legally.
