When Devin Patrick Kelley took a Ruger AR-556 semiautomatic assault rifle to the First Baptist Church in Sutherland Springs, Tex., last November, he brought 15 high-capacity magazines that each contained 30 bullets.

How many did he empty?

“All of them,” a Texas law enforcement official said at a news conference in the days after the massacre.

If William B. Ruger Sr., the co-founder of the gun maker Sturm, Ruger & Company, had had his way, Mr. Kelley’s firepower might have been much diminished. In 1989, Mr. Ruger proposed a ban on high-capacity magazines, which led a smaller rival to call Sturm, Ruger “the Benedict Arnold of the gun industry.”

Mr. Ruger once said that he was open even to waiting periods for handgun purchases. “If the truth be known, I see no real harm in the concept,” he said, but cautioned, “the trouble is, where does it end?”