One big advantage the gun lobby used to claim was the willingness of its fervent base to take direct action to support the cause. Guns become central to the political affiliations of many firearm owners, who have been more likely than reform advocates to give money or contact politicians to try to influence policy.

Now, we have some of the first, tangible evidence of how the youth-led movement that has sprung from the Parkland shooting has increased the grassroots muscle of the anti-gun violence side. It’s found in the comments that Americans have filed with the federal government to express their views of the Department of Justice’s proposed restrictions on bump stocks, the aftermarket devices that allow common semiautomatic rifles to fire more than 500 times per minute.

The government has taken two rounds of public comments on plans by the Bureau of Alcohol, Tobacco, Firearms and Explosives to regulate bump stocks, which were made infamous by their use in the Las Vegas mass shooting last October. According to a Trace analysis, pro-regulation messages flooded the more recent comment window — a complete reversal of sentiment from the first round of feedback.

Only 13 percent of comments on the initial ATF proposal expressed support for limiting access to bump stocks, which can currently be purchased without a background check.

For the second measure, supporters of regulation outnumbers opponents nearly three to one.

The ATF first announced in December that it would explore reclassifying bump stocks as machine guns, a move that would subject the devices to much stricter regulations and effectively prohibit civilian ownership.

Late last year, the ATF submitted what’s known as an advanced notice of its intention to regulate the devices, a process that requires public input. The agency solicited responses from manufacturers, retailers, and consumers of the devices.

All told, the first comment period attracted more than 30,000 responses. The vast majority — 85 percent — opposed the proposed regulation, The Trace found.

On March 29, six weeks after the Parkland school shooting launched a student-led gun reform movement, the ATF issued its official proposal for the regulation, accompanied by a new call for public comment, this time geared toward “all interested parties” and closing on June 27.

The Trace downloaded the text of more than 94,000 of the comments the bureau received and analyzed them for trends and general sentiment. More than 72 percent of the comments expressed support for regulating bump stocks. The new figure closely matches levels of support found in public polls on the subject.

The Parkland activists appear to have been a driving force behind the surge in support for the regulation. Nearly 14,000 comments poured in between May 19 and 20, coinciding with viral tweets posted by organizers David Hogg and Emma González.

“This reversal is quite something — and yet more evidence that gun regulation advocates are closing the participation gap that has historically advantaged gun rights supporters,” said Kristin Goss, professor of political science at Duke.

Donald Haider-Markel, professor and chair of political science at the University of Kansas, says that the Parkland students’ identity as survivors of a mass shooting, and their effective use of social media, can give their calls to action significant traction.

“Rather than a specific message,” he said, “you could argue that it might be more the messengers, as well as their level of continued engagement.”

About a quarter of all comments were submitted in the final three days of the comment period, during which time the proposed bump stock restrictions received support from Congresswoman Tulsi Gabbard, actresses Amy Schumer and Julianne Moore, gun advocacy group Moms Demand Action, and petition site

The gun-rights group Gun Owners of America, framing the measure as a threat to all semiautomatic weapons, also rallied its followers on Facebook and with alerts published on its website, which resulted in periodic surges of comments opposing the regulation.

A large share of responses received in both public comment periods contained text sourced — in whole or in part — from form letters promoted by advocacy groups on both sides. The most widely replicated messages were produced by the gun control organization Giffords, making up 12 percent of all comments, and Gun Owners of America, with 11 percent.

The Trace randomly selected and reviewed 1,000 comments that were not derived from form letters to assess the views of Americans who sent the ATF feedback they had drafted themselves. Eighty percent of these original comments were in favor of the regulation, with 19 percent opposed. Another 1 percent did not express a discernible stance.

Now that the public comment period has concluded, the ATF will review the feedback and decide whether to withdraw, revise, or proceed with the proposed regulation.

Unwilling to wait for the Department of Justice to complete its lengthy process, eight states have moved to ban bump stocks on their own.