SACRAMENTO, Calif. (AP) — California gun owners starting Thursday are getting a second chance to register and keep a type of firearm that is now illegal to buy under the state's expanded definition of assault weapons.

The registration period is for those who legally bought so-called bullet-button assault weapons.

The bullet buttons allow users to rapidly exchange ammunition magazines by using a small tool or the tip of a bullet.

California lawmakers outlawed weapons with that feature in 2016. But those who bought them before the law took effect on Jan. 1, 2017, are still allowed to own them, so long as they register the weapons with the state.

It's the second time the state has opened a registration window after critics said it botched the first try in 2018. Gunowners said the state's online registration system crashed or timed out as they repeatedly tried to register their weapons using different web browsers, hardware and multiple devices.

The state attorney general's office settled a resulting lawsuit in March by agreeing to reopen the registration window and not hold any owners liable for missing the July 1, 2018, registration deadline.

An attorney for the gun owners, George M. Lee, estimated at the time that the do-over will apply to "possibly tens of thousands of gun owners."

The new registration window will run from 9 a.m. Thursday until 9 a.m. April 12.

Owners will have to assert under penalty of perjury that they tried to register their weapon before the original 2018 registration deadline but could not because of technical difficulties.