A bill that would ban the sale, manufacture, importation and transfer of assault weapons — and define what those firearms are — will soon enter the gun regulation debate at the Colorado Capitol.

The proposal, sponsored by Democratic state Reps. Andrew Boesenecker and Elisabeth Epps, drops earlier draft language that would have outright banned possession of those types of firearms. Conservative groups published the earlier version, which Boesenecker called a “snapshot in time” as they worked through the proposal. Advocates dropped that provision out of concerns of enforceability.

Instead, sponsors focused on the sale and transfer of weapons capable of shooting a lot of bullets quickly — or capable of being modified to do that, Boesenecker, who represents Fort Collins, said. The goal is to blunt access to the types of firearms used in the mass shootings at the Boulder King Soopers in March 2021 and Club Q in November. He said he began working on the proposal before the Club Q massacre.

“If you are the legal owner of an assault weapon today, nothing changes for you in our state,” Boesenecker said of the proposal. “We’re really focused on creating a moment between a motive to do something harmful to yourself or your community, and the moment where you can readily acquire the firearm to do it.”

The bill hasn’t been formally introduced yet, but should be soon, he said. Boesenecker had previously declined to comment on the leaked draft that included the possession ban.

Some of the features that would classify a gun as an assault weapon under the bill include semi-automatic rifles with a detachable ammunition magazine plus one of the following: A pistol grip; a protruding grip for the non-trigger hand; a folding, telescoping or detachable stock that can enhance the ability to conceal the weapon; a barrel shroud; or flash suppressor, among others.

It would include semi-automatic pistols in the assault weapon definitions if they can have a second pistol grip, the ability to accept a magazine or ammunition feeding device in a place other than the pistol grip, weighs more than 50 ounces unloaded or includes an arm brace or similar accessory that extends horizontally behind the grip, among other provisions.

Because firearms vary so much and can be modified in so many ways, defining what constitutes an assault weapon has been a point of contention. He said these features and others included in the definitions are those that allow people “to fire a large amount of ammunition very quickly.”

Boesenecker said the bill’s language doesn’t affect the sale or transfer of “firearms that we would typically think of in a concealed carry or self-defense situation,” such as a semi-automatic handgun with a magazine that loads in the grip.

“We know that these are very close models of weapons of war,” Boesenecker said. “… At the very least, that is their intended purpose, first and foremost. We know that regulations and prohibitions in this space save lives.”

He cited a 2018 study by the Rand Corporation, which was updated this month, that found even state-level weapon bans reduce mass shooting deaths to 55% of what’s expected without the bans.

Boesnecker said he grew up shooting pistols for target practice and remembers schools clearing out during deer season. He still owns firearms and enjoys target shooting, he said — but also believes steps can be taken to prevent gun violence that doesn’t impede Coloradans’ Second Amendment rights.

He acknowledged that neighboring states don’t have — and have little to no likelihood of enacting — these types of restrictions and that it would take federal action to close that avenue. Regardless of other states, Boesenecker said Colorado can take its own steps.

The bill will likely be one of several proposed gun regulations introduced this session. Gov. Jared Polis, also a Democrat, has specifically called for lawmakers to look at expanding the extreme risk protection order, or red flag, law and to address so-called ghost guns.

The pro-gun rights advocacy group Rocky Mountain Gun Owners has already pledged to sue over any firearm law it sees as overstepping Second Amendment rights. Boesenecker said they crafted the bill with recent pro-gun rights U.S. Supreme Court rulings in mind.

He noted that Illinois passed a similar bill — with some of the same definitions — though it is also facing its own legal challenges. Nine states, plus Washington, D.C., have some version of an assault weapons ban.

Colorado’s Republican lawmakers have also staked their support for gun owners’ rights, though they hold a superminority in the state House of Representatives and a near-superminority in the Senate.

“What we’ve seen and heard should worry every law-abiding gun owner in Colorado,” House Minority Leader Mike Lynch, a Wellington Republican, said.

He noted that no gun legislation has been formally introduced, but “some rumored legislation appears so radical even the governor won’t agree to these concepts publically.” Polis has kept his remarks around firearms — including when specifically asked about assault weapon bans — to his support for the red flag law, background checks, and laws around ghost guns.