From Seattle Times:

“Gun violence is very expensive,” Burgess said, noting that the direct medical costs of treating 253 gunshot victims at Seattle’s Harborview Medical Center last year surpassed $17 million, with taxpayers covering more than $12 million of that. “It’s time for the gun industry to help defray those costs and this is a very reasonable way to do it.”

The tax, imposed on gun sellers, would be $25 on each firearm sold in the city and five cents on each round of ammunition.

 Sales of antique firearms and some other sales could see relief from the tax while individuals selling no more than one gun per quarter would be exempted.