A certain president is mistakenly remembered as being pro second amendment, but he wasn't. He was pro law enforcement was a big proponent of banning "cop killer" bullets designed to penetrate body armor. He was the genesis of most of the media hype.

The problem with banning bullets based on ability to penetrate body armor is that almost any centerfire rifle cartridge will go through Level IIIa body armor like a hot knife through butter.

In addition, some pistol rounds will go through body armor when fired out of a rifle at much higher velocities. For example, Level IIIa armor will stop a 158 gr JSP fired out of a 4" revolver, but that same round will launch at just over 1800 fps in a 20" carbine, and will defeat Level IIIa armor.

There is also a great deal of cross over between pistol and rifle rounds, so the "capable of being fired in a pistol" language still makes rounds like the .22 Magnum, .223, .30-30, as well as larger rounds like the .308, .30-06 and the .45-70 fall into the category of "pistol" rounds.

All three of the above issues make it very hard to define "armor piercing" in any meaningful way - other than as a way to ban large swaths of ammunition.

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Several years ago the ATF rewrote its definition of "armor piercing" in an effort to ban M855 ball ammo as it has a steel penetrator. Since the end result was a significant change in how a regulation was interpreted it had to go out for public comment. Fortunately, ATF received over 90,000 negative public comments and rescinded the proposed change.

One of the key points was simply that criminals are not shooting people with M855. Another key point was that in terms of Level IIIa body armor, if they were shooting a .223 rifle, it really didn't matter what round they shot in it, it was going to defeat the armor - period.