Gun control activists notched their most significant legislative win of the year on Wednesday when Washington Gov. Jay Inslee signed a bill banning the sale or purchase of “high capacity” magazines in the state; a top priority for anti-gun groups in the state as well as Washington Attorney General Bob Ferguson, who had unsuccessfully pushed the measure in previous sessions only to see the new restriction be approved on party lines in the legislature a few weeks ago.

The signing ceremony held by Inslee featured a number of gun control supporters, including members of Moms Demand Action, but the general public wasn’t allowed to attend. In fact, the state capitol was closed to the public for several hours before and after the bill signing; a measure the Washington State patrol described as a “prudent precaution.”

Inslee may have been worried about gun owners crashing his party to protest the magazine ban, but now that his dog-and-pony show is complete he should be much more concerned about what he’s going to tell voters when Washington’s newest gun control law does jack squat to reduce violent crime.

The new law also makes selling a prohibited magazine or offering one for distribution or sale a violation of Washington’s Consumer Protection Act, which allows the attorney general’s office to take action on alleged violations of the act to get restitution and civil penalties.

The bill signed into law doesn’t bar the possession of 10+ round magazines that were purchased before ban takes effect; a watering-down of the magazine bans that have been approved in recent years in states like California and New Jersey that require existing magazine owners to permanently modify them or get rid of their property in order to remain in compliance with the law.

Those laws are both facing legal challenges, and that’s also going to be the case with the new law in Washington State.

In a statement issued after the bill signing, the Sacramento, California-based Firearms Policy Coalition said that it plans to lead a lawsuit over the new law, saying that it “condemns this latest act of state aggression and will not allow this law to go unchallenged.” The group said it was looking for Washington residents who could be potential plaintiffs in the planned action.

Ferguson said that he was confident that the ban was constitutional and that his office could successfully defend any potential litigation. He pointed to appellate history with other states with bans, including California, where the 9th Circuit Court of Appeals overturned a ruling by two of its judges and upheld California’s law in November.

The Second Amendment Foundation has also signaled that it will be filing suit over the new law, and while Bob Ferguson may claim to be confident that the ban will be upheld, he shouldn’t get too comfortable. Yes, the Ninth Circuit will uphold the law, because the Ninth Circuit has never come across a gun control law that it found to be unconstitutional. But the Ninth Circuit doesn’t have the final say, and frankly, while I have my own bias I also believe that opponents of these kinds of bans have the better argument.

The Supreme Court has said that arms that are in common use for lawful purposes are protected by the Second Amendment, and there’s no question that magazines that can hold more than ten rounds are in common use, with more than 80-million magazines capable of holding 30-rounds or more already in the hands of American gun owners. The number of 10+ round magazines possessed by law-abiding Americans is well over 100-million, and the men and women who own them use them for a variety of lawful purposes, including self-defense, training, competition, and hunting.

That alone should be enough to throw out Washington’s law, even if the case has to go to SCOTUS in order for that to happen. And with challenges to California and New Jersey’s bans already awaiting the Court’s consideration, Washington State’s new gun ban could end up tossed sooner than we think.