Colorado lawmakers are closing in on limiting sales of semiautomatic firearms — including those commonly known as assault weapons — in the state after two years of unsuccessful attempts.

Senate Bill 3 passed the state Senate last month after coming in for some heavy amendments that would allow otherwise-banned guns to be sold to people who complete training and a background check. The measure is set for a first committee vote in the House on Tuesday before it moves to the full chamber.

Though Republicans have promised to fight the bill and gun-rights groups have pledged to sue, should it pass, the proposal has sufficient Democratic support to clear the legislature and head to Gov. Jared Polis.

Polis, a Democrat, was leery of the stronger version of the bill but is now expected to sign it, said Rep. Andrew Boesenecker, a Fort Collins Democrat and one of the bill’s sponsors. The measure would be the most sweeping gun-control law adopted in the state, even amid Democrats’ many recent efforts to tighten firearm regulations in Colorado.

Here’s a closer look at the bill — and the debate around it.

What exactly would the bill do?

Now that’s it been amended, SB-3 would generally limit the sale of certain semiautomatic firearms that accept detachable magazines and are gas-operated. That applies to the group of guns that are colloquially known as “assault weapons,” such as the AR-15 rifle.

There are loopholes. At the behest of Polis and some moderate Senate Democrats, the bill was amended so it would still allow people to purchase the otherwise-banned firearms under certain conditions. If buyers had previously passed a hunter’s education course, they would need to take a four-hour training session. If they hadn’t, they’d need a 12-hour course.

They would then need to be fingerprinted and background-checked by their county sheriff in a process that’s identical to obtaining a concealed-carry permit. That process includes ensuring a person doesn’t have a substance-use disorder and isn’t the subject of a protection order, among other things. The sheriff can also determine if people are a danger to themselves or others; if they are, the sheriff can withhold approval cards.

The measure would ban firearm components that make semiautomatic weapons fire faster. That includes bump stocks, which were briefly banned federally after they were used in the 2017 Las Vegas shooting, America’s deadliest mass shooting.

The sale of those components would be banned flat out, regardless of a person’s training or vetting.

Where does Polis stand?

Asked by The Denver Post if the governor now supported the bill, a Polis spokesman said the governor “appreciates” that lawmakers worked with his office on amendments to address gun violence and uphold “our freedom and Colorado’s rich hunting and sport shooting culture.”

Would the bill outlaw possession or require people to turn over their guns?

No. The bill applies only to the sale, purchase, transfer and manufacture of the weapons. It would not be illegal to possess any of the banned firearms, and anyone who owns them now — or before the law would go into effect on Sept. 1 — would be able to keep them without any additional training required.

Gun stores have warned that the proposal would harm their businesses, given the popularity of the AR-15 and other covered guns, though the exemptions would still allow them to be sold to approved customers.

Which guns are covered?

The bill applies mostly to gas-operated, semiautomatic weapons that accept detachable magazines. That essentially covers most — if not all — of the so-called assault weapons common in mass shootings, like the AR-15 and similar guns, two experts told The Post.

Those weapons work by recycling the gas created when the bullet is fired to then cycle the gun and ready it to fire again. They also generally take detachable magazines — which can be rapidly swapped out and, in the case of high-capacity magazines, have been banned in the state for more than a decade.

Another amendment added in the Senate exempted a list of common rifles, some of which are used for hunting. Those include some guns that are old enough to have seen action in World War II. But it also includes weapons that are substantially similar to the AR-15, said Aaron Brudenell, a forensic science consultant and firearms expert who conducts trainings for the Bureau of Alcohol, Tobacco, Firearms and Explosives.

Broadly speaking, the bill wouldn’t apply to common handguns, revolvers or shotguns. Most common semiautomatic pistols — like Glocks — are operated by their own recoil, not recycled gas, and thus wouldn’t be covered.

But the bill sponsors are also seeking to curtail pistol variants of the AR-15, the measure would cover some handguns, like James Bond’s Walther PPK. Those handguns use the same operating system as AR-variant pistols, like the one used by the shooter at the Boulder King Soopers in 2021, and would thus be caught in the crossfire of the bill’s efforts to block those weapons.

Brudenell questioned whether the bill could be stretched to cover other common handguns, though the bill’s sponsors and advocates have been adamant it would not.

Boesenecker acknowledged that “a relatively small portion of the (handgun) market” would be covered by the bill, but he said those guns have available alternatives that wouldn’t be affected.

So, then, is this a ban?

That’s a tricky question. The bill was initially described by its sponsors as a way to enforce the state’s 2013 high-capacity magazine ban. But now that the bill would still allow weapons that accept those components to be sold, that argument has lost some ground.

It’s also not quite a ban, since Coloradans could buy AR-15s under the law so long as they passed a training requirement and background vetting.

But such an argument won’t assuage gun-rights groups, which argue that their ability to purchase firearms shouldn’t be infringed at all.

And the loopholes have led to some teeth gritting from the bill’s supporters: After the measure was weakened in the Senate, the advocacy group Moms Demand Action said it “strongly preferred” the first version but was still happy with the bill’s present state.

How would Colorado’s law stack up?

A number of states have enacted bans on so-called assault weapons, and others have adopted vetting and training requirements before a person can purchase specific weapons, said Alison Shih, senior counsel for Everytown for Gun Safety, which is backing the bill.

“Many other states have some kind of permit-to-purchase (requirement) for firearms, and many of them have them for all firearms,” she said. “… A third of the U.S. population lives in a state that outright bans a subset of military-style firearms.”

SB-3 is unique in that it would limit the sale of those controversial firearms unless a person is trained and vetted, said Andrew Willinger, the executive director of the Center for Firearms Law at Duke University School of Law.

It’s also unique in that it focuses on certain components — like gas operation and detachable magazines, he said. Other states ban a list of specific weapons, and past unsuccessful bills in the Colorado legislature took that approach.

Is any of this constitutional?

Should this bill reach Polis’ desk and be signed into law, it would almost certainly be challenged immediately in court.

Willinger said the bill was likely on solid constitutional footing, even in a judicial system topped by a conservative U.S. Supreme Court that’s taken a more expansive view of the Second Amendment. The high court turned away recent challenges to other gun control bills — including a weapons ban and a permitting requirement — and lower courts have upheld the laws in other states, Willinger and Shih said.

Still, Shih and Willinger said they expected the Supreme Court to take up an assault weapons case at some point.

Willinger said the training and vetting requirements added in the Colorado Senate likely put the bill on even firmer ground under the Supreme Court’s 2022 Bruen decision, which further expanded gun rights. (Shih said Everytown was confident the original bill would’ve been upheld, too.)

“I suspect the court will take a case like that at some point, but I think the analysis is really quite different when you think about the one Colorado is considering,” Willinger said. “You then basically have an argument that the state can make — that this is just akin to the type of objective licensing approach that states use for conceal-carry, for example. The only thing you have to do is just comply with the series of objective requirements, taking these classes and so on.”