Investigators say the gunman in the deadly Las Vegas shooting, Stephen Paddock, had two devices called "bump stocks."
They are used to make semi-automatic guns function much like automatic weapons.
The "bump-stock" modifications are completely legal in Texas because they change the way a finger pulls the trigger but don't actually modify the weapon.
David Prince, of Eagle Gun Range in Farmers Branch, explained the natural kick of the gun reacts with the trigger finger to fire the weapon more quickly.
Some gun owners say the modifications are mainly used for recreational reasons, as they make the weapon less accurate.
"Of the tens of thousands of people that come into this range, we probably only have one or two that have this [bump stock]," Prince said. "They don't see the need for it. It's really finicky [and] a little bit contrary on how to make it operate. It takes a lot of practice to make it efficient."