Maryland outlawed "rapid fire trigger activators" ("devices that, when attached to a firearm, increase its rate of fire or trigger activation"). Under the law, it is now a crime to "manufacture, possess, sell, offer to sell, transfer, purchase, or receive" that kind of device, and you can't transport one into the state. The plaintiffs are individuals who owned a device, plus an organization (Maryland Shall Issue, Inc.).

In Maryland Shall Issue, Inc. v. Hogan, the U.S. Court of Appeals held there was not a taking under either the Fifth or Fourteenth Amendment, or the Maryland Constitution. And MSI, Inc. didn't have organizational standing.

The takings analysis focused on the lack of a physical taking, concluding that by outlawing previously lawful personal property, the state did not seize personal property (which is subject to a high degree of government control and regulation). The court noted its earlier decision (Holliday Amusement Co. of Charleston, Inc. v. South Carolina) which held that banning possession or sale of gambling machines was not a taking. The owners asserted that the U.S. Supreme Court’s ruling in Horne changed that, but the Fourth Circuit held no: in Horne, the raisins were actually turned over to the government, while here, Maryland didn't say "give us your rapid fire devices," it said only that you couldn't continue to possess them:

Appellants overlook this distinction and how it applies in this case. SB-707 does not require owners of rapid fire trigger activators to turn them over to the Government or to a third party. Regardless of whether we would today decide Holliday -- which required forfeiture of the gambling machines -- the same way, the Horne Court expressly preserved the reasoning behind Holliday’s conclusion as it appears in Lucas and Andrus. Though SB-707 may make the personal property economically worthless, owners are “aware of th[at] possibility” in areas where the State has a “traditionally high degree of control.” Lucas, 505 U.S. at 1027–28. We can think of few types of personal property that are more heavily regulated than the types of devices that are prohibited by SB-707. And, “government regulation—by definition—involves the adjustment of rights for the public good.” Andrus, 444 U.S. at 65.

That distinction was something that should not have made any difference, according to the dissent by Judge Richardson (which seems to have been drafted as if it may be a majority opinion in the future), which argued that the owners were ousted from possession, and that's a "classic" taking. The entire dissent is worth reading, especially this part:

You might wonder how a singular constitutional clause can be imbibed with such disparate meanings. I might too. One meaning is rooted in the original understanding of a taking, see Horne, 135 S. Ct. at 2426–27; compare 1 William Blackstone Commentaries 134–36 (1st ed. 1765), the other is a newer doctrine shaped by the forward-march of government regulation during the twentieth century, see Murr, 137 S. Ct. at 1942. But students of the law are no stranger to parallel legal theories that spring from the same constitutional source. See, e.g., Kyllo v. United States, 533 U.S. 27, 34 (2001) (noting the Fourth Amendment shelters privacy interests “that existed when the Fourth Amendment was adopted” as well as contemporary “reasonable expectations of privacy”). In this respect, the Takings Clause is simply par for the course.

But by applying distinct legal rules in the classic- and regulatory-takings contexts, the Supreme Court has concentrated considerable pressure on the threshold question of categorization. In this case, that pressure comes to a head. Plaintiffs argue Maryland’s ban amounts to either a per se classic taking (see Loretto/Horne) or a total regulatory taking (see Lucas). If Maryland’s ban is a taking within the former framework, just compensation is required—no matter the state’s interest. But if Maryland’s ban is more aptly characterized as a total regulatory taking, then background principles of Maryland law likely defeat Plaintiffs’ takings claim. See Majority Op. 15–17; Holliday Amusement, 493 F.3d at 410–11. But see Duncan v. Becerra, 265 F. Supp. 3d 1106, 1136–39 (S.D. Cal. 2017), aff’d, 742 F. App’x 218 (9th Cir. 2018). This stark doctrinal divide requires confronting the deceptively difficult question of whether Maryland’s ban falls within the scope of the classic-takings doctrine. I conclude it does.

With a well-reasoned dissent and some logical and legal holes in the majority opinion, we expect more: an en banc petition and maybe a cert petition.