OLYMPIA — Sponsors of a proposed initiative to put new restrictions on sales of semiautomatic assault rifles began gathering signatures Thursday.

But they are going to have to work fast if they want to get it on the November ballot.

To qualify, they must collect and turn in signatures of 259,622 registered Washington voters by July 6. They will probably need to turn in closer to 350,000 to account for any invalid or duplicate signatures.

“We’re confident we’ll be able to gather what we need,” said Renee Hopkins, chief executive officer for the Alliance for Gun Responsibility, which is behind the measure. “We’ve been hard at work gearing up for a highly visible signature gathering drive over the next four weeks.”

As proposed, Initiative 1639 would raise the age for buying a semiautomatic rifle from 18 to 21, which is the age required to buy a handgun. It also would require the same background check and waiting period for those rifles as with handguns.

The measure would require completion of a firearm safety training course, hold gun owners liable if their unsecured firearm is used to harm themselves or others and add wording to the purchase paperwork cautioning buyers that a firearm in the home increases the “risk of death to self and others.”

Backers of the measure started circulating petitions a few hours after Thurston County Superior Court Judge Carol Murphy approved how the measure would be described on the ballot.

The Alliance, the NRA and two citizens, Glen Morgan and Joe Wilson, each challenged wording proposed by the Office of the Attorney General. Murphy made a few revisions at the conclusion of a three-hour morning hearing.

“We’re satisfied with the judge’s ruling and now we just need to get into the field and start gathering signatures, which we’ll be doing tonight,” Hopkins said.

To supplement volunteers, professional signature-gatherers will be hired and could wind up earning in the neighborhood of $10 a signature because of the short time frame.

Money isn’t a problem right now. The alliance has already lined up $2.5 million in contributions and pledges for this effort, including $1 million apiece from Microsoft founder Paul Allen and venture capitalist Nick Hanauer.

This is the same group that passed ballot measures in 2014 to require universal background checks and in 2016 to create the extreme risk protection orders.

Jerry Cornfield: 360-352-8623; jcornfield@herald net.com. Twitter: @dospueblos.