You can’t any more than Obama could.
Via Reason:
Today President Trump said he plans to prohibit bump stocks by executive order, notwithstanding the lack of legal authority to impose such an administrative ban. “We can do that with an executive order,” Trump told Sen. John Cornyn (R-Texas). “I’m going to write the bump stock, essentially, write it out. So you won’t have to worry about bump stock[s]. Shortly that will be gone.” Trump’s determination to ban bump stocks by administrative fiat is a blatantly political attack on the rule of law that conservatives would have immediately condemned as such if Barack Obama had attempted it.
Bump stocks are accessories that increase a rifle’s rate of fire by harnessing recoil energy to help the shooter slide the weapon back and forth against his trigger finger. Previously an obscure novelty, they became notorious after they were used in the mass shooting that killed 58 people in Las Vegas last year. People who had never heard of bump stocks before, including conservatives who are otherwise leery of gun control, were suddenly clamoring for a ban. Even the National Rifle Association seemed to favor a ban, urging the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) to “immediately review whether these devices comply with federal law.” Talk of banning bump stocks picked up again after this month’s mass shooting at a high school in Florida, although that attack did not involve bump stocks.
While bump stocks became a bête noire of the anti-gun movement only recently, they were never the sort of product that gun controllers would happily tolerate. It is therefore telling that the Obama administration, which was much less supportive of gun rights than the Trump administration, never tried to restrict bump stocks. To the contrary, the ATF during the Obama administration repeatedly affirmed their legality—in a 2010 letter to Slide Fire Solutions, which makes one version; a 2012 letter to a competing company, Bump Fire Systems; and a 2013 response to an inquiry from Rep. Ed Perlmutter (D-Colo.). As the agency explained to Perlmutter, “Bump-fire stocks (such as the Slide Fire Solutions stock) that ATF determined to be unable to convert a weapon to shoot automatically were not classified as machineguns.”