Ah, but to ban a thing, you have to define that thing you are banning. If I say "shotguns are illegal", I have to define what a "shotgun" is. (In Indiana, that would be covered by IC 35-47-1-11.)
So, this law intended to ban "armor piercing handgun ammunition", but it had to define exactly what "armor piercing handgun ammunition" was. Like it or not, they picked a definition that was "ammunition that can be fired from a handgun that is made out of thus and such materials". If there were no .223 pistols, we couldn't be having this discussion because everybody and their brother knows that rifle rounds go through body armor. However...
The solution, of course, is to repeal the damn law. (Unless joshs or someone thinks it has a hope in hell of getting shot down as overbroad in court.)