Some Washington gun store owners believe there will be an increase in gun sales before Initiative 1639 goes into effect on July 1.

Washington gun shop owners expect an increase in sales after state voters approved an initiative that adds restrictions to the purchase of semi-automatic rifles.

Voters last week passed Initiative 1639, which will raise the purchase age for semi-automatic rifles to 21.

Starting next year, buyers will be required to pass an enhanced background check and prove they have taken a firearms-training course. They must wait 10 business days to take possession of the gun.

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"The response to this is always classic," Wade Gaughran, owner of Wade's Eastside Guns, told the Seattle Times. "People will buy guns to beat the deadline."

The initiative also authorizes the state to require gun sellers to add $25 to sales of semi-automatic rifles to pay for new regulations.

Under a "safe storage" provision, gun owners could face criminal penalties if someone not legally allowed to have the rifles, such as a child or felon, gains access to them and fires the gun or uses it in a crime. The safe storage provision does not apply if the gun was secured with a trigger lock or similar device or if the owner had reported it stolen within five days.

"We will see people speed up their gun purchases," Gaughran said. "(Buyers will say) 'I'll buy the next year or two of my gun budget in the next few months just so I can bypass this law for as long as possible.'"

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The Alliance for Gun Responsibility advocated for the initiative. Spokesman Tallman Trask said new regulations can lead to increased sales but the initiative will not lead to "onerous restrictions."

"What it really boils down to is people are a little unsure of how to respond to new regulations and they go out and buy new firearms," Trask said. "It's unfortunate."

Gun dealers want clarity from state regulators on parts of the new law such as the training requirement. Buyers must show they have completed a "recognized firearm safety training program" in the last five years that covers issues such as handling, storage and suicide prevention. The training must be sponsored by a law-enforcement agency, college or university, nationally recognized organization or firearms training school.

Gaughran said his store may develop a "quick test" to administer at the counter or online.

Some parts of the country reported a slump in gun sales following the election of President Donald Trump. Jason Cazes, owner of LowPriceGuns.com in Bellevue, increased his inventory because he anticipated Trump would lose to Hillary Clinton.

"Here's what drives sales in the gun business: the possibility of regulation coming or fear in the world," Cazes said. "This summer was the worst summer I've ever had in sales."

Bruce Smith, manager of Surplus Ammo and Arms in Tacoma, said he's seen a small increase in business and questions since the election but "it hasn't been crazy because it's not federal."