“I own a lot of guns, and as a hunter and sportsman, I think that’s our right as Americans, but I don’t understand the use of this bump stock,” Senator John Cornyn of Texas, the No. 2 Republican in the Senate, said, adding, “It seems like it’s an obvious area we ought to explore and see if it’s something Congress needs to act on.”

Mr. Cornyn said the continuing legality of the conversion kits was “a legitimate question,” and told reporters he had asked Senator Charles E. Grassley of Iowa, the Judiciary Committee chairman, to convene a hearing on that issue and any others that arise out of the Las Vegas investigation.

Other Republican senators, including Lindsey Graham of South Carolina, Orrin G. Hatch of Utah and Marco Rubio of Florida, said they would be open to considering legislation on bump stocks.