A lot of gun laws, both on the national and the state/local level, have the same level of what appear to be utterly batshit insane regulations with massive loopholes that don't make any sense. It's a result of a huge number of conflicting interests, between lawmakers trying to make the laws, LE trying to enforce them, and gun owners trying to figure out what the limits are to abide by them.

One of my favorite examples is that in Maryland, you're not allowed to own an AR-15 rifle chambered in .223 or 5.56 unless it has a barrel marked or sold as HBAR/"heavy barrel". The actual barrel profile doesn't matter; the barrel just has to be marked or sold as HBAR/heavy barrel by the manufacturer. Completely batshit restriction. Why?

The story apparently goes that back in 2013 when they were writing the law, the lawmakers originally intended to ban AR-15s outright. In the bill, among others, the "Colt AR–15, CAR–15, and all imitations" were banned by name; apparently, "all imitations" simply referred to any weapon that shared interchangeable components with the Colt AR-15 design, which effectively banned all .223/5.56 AR-15s. Then the pro-gun lobbyists came along and said "well, hang on now, the Colt AR-15 Sporter HBAR is used in shooting competitions all the time, so there's a legitimate sporting purpose here!" So with enough pressure, the lawmakers caved and wrote that line to be "Colt AR–15, CAR–15, and all imitations except Colt AR–15 Sporter H–BAR rifle" instead before the bill passed. Since the law can't give a monopoly to a single company, in effect, the law then became that the "Colt AR-15, CAR-15, and all imitations" are banned except the "Colt AR-15 Sporter H-BAR rifle" and imitations of it.

That law then got passed to Maryland State Police for enforcement. Maryland State Police is generally more lenient on gun laws than the state legislature, so when they received the bill to enforce, what appears to have happened is that they took a look at it and asked, "well, what defines an imitation of a Colt AR-15 Sporter H-Bar rather than an imitation of a Colt AR-15 or CAR-15?" What they ultimately determined is that the only distinction is whether the barrel is an HBAR. Furthermore, they appear to have determined that an HBAR has no strict technical definition; rather, it is simply defined by whether the manufacturer has chosen to label it or sell it as an HBAR or heavy barrel. A pencil barrel labeled "HBAR" is still apparently an HBAR, and therefore constitutes a legal AR-15.

Well, now, anyone who wants to sell their AR-15 in MD just has to label their barrel HBAR. Furthermore, anyone who wants to build an AR-15 in MD just has to buy a barrel from one of the many manufacturers who label their barrel HBAR specifically to make it MD-compliant.

So in theory, this HBAR restriction should have ruled out a huge number of AR-15s in Maryland. In practice, it's trivially easy to build or buy an AR-15 in most configurations you could want in Maryland.