Quite a few inaccuracies but I’ll cover only the biggest you made.

“ There are armor-piercing .223 rounds (supposedly “green tip”) that have a hardened steel core. Those are absolutely forbidden on all but one of our ranges (and, illegal to own) because, while our range shoots down a point into the Pacific, those rounds are able to pass through several types of target structures & safety areas. (Yes, humans do remain on the range for certain tasks, like refilling plate-drop pistol targets. Armor-piercing rounds will go right through those safety sheds.)”

Green-tip M855 is not armor piercing. It does not have a hardened steel core, it has a mild steel tip. It never has been and does not meet the ATF requirements to be considered armor piercing. M855 came from the development of the FN Minimi (adopted as the M249 SAW) and some of its particular requirements. M855A1 which is a more advanced design and is currently issued to downrange combat troops is also not armor piercing. There is an armor piercing 5.56mm NATO cartidge and in 18+ years in the service I have never come across it being issued for training or operational usage. Most full power rifle cartridges exceed the penetrating capability of M855, some outdoor ranges don’t allow them because the unhardened mild steel tip can spark and ignite a fire.

“One of our recent problems has been the creation of Titanium studs cast into a .223 round — non-magnetic, they are all but undetectable.”

There is no such ammo available. Titanium is a relatively soft metal, expensive, and would have poor ballistic behavior compared to other metals.

“ Friends, thieves, and certain classes of people who load their own ammunition either have access to, or else, make these rounds. They will easily pierce all but the heaviest ceramic plate in standard Class III body armor. That’s a round that will easily pierce 4–5 SOCAL townhouses & almost anything inside along the path.””

I reload my own ammo for all of my rifles and never have I seen AP bullets available except for small quantities of M2AP “pulls”. The only AP ammo that is legally available through normal channels is mil-surplus M2 AP that was issued when the M1 Garand was still the active service rifle. NIJ Level IV conditioned armor is rated to stop M2 AP. High powered magnum grade rifles can defeat Level IV armor without AP bullets.