Web sites now advertise overnight UPS delivery of the clips, which carry up to 40 rounds for both semi-automatic rifles, including 9mm pistols, and handguns.
"High capacity magazines read extreme firepower and gusto. Stock Up!" is the headline of one of many gun shop Web sites.
Virginia law enforcement officials have not identified the weapon used in the shootings today at Virginia Tech, but gun experts say the number of shots fired indicate, at the very least, that the gunman had large quantities of ammunition.
"When you have a weapon that can shoot off 20, 30 rounds very quickly, you're going to have a lot more injuries," said Paul Helmke of the Brady Campaign to Prevent Gun Violence.
"It's not one or two shots at a time when you're putting 20 bullets, spraying them into a classroom or into a dorm room," Helmke said.