This week, he also used Twitter to respond to the Colorado massacre with a similar demand. “Because of the Aurora, Colo., tragedy, the American Congress must review its mistaken legislation on guns,” he wrote. “It’s doing damage to us all.”

The United States-Mexico gun divide was not always so wide. Article 10 of Mexico’s 1857 Constitution declared, much like the American Second Amendment, that “every man has the right to bear arms for his security and legitimate defense.” But since then, the country has veered from the American model.

The 1917 Constitution written after Mexico’s bloody revolution, for example, says that the right to carry arms excludes those weapons forbidden by law or reserved for use by the military, and it also states that “they may not carry arms within inhabited places without complying with police regulations.”

The government added more specific limits after the uprisings in the 1960s, when students looted gun stores in Mexico City. So under current law, typical customers like Rafael Vargas, 43, a businessman from Morelos who said he was buying a pistol “to make sure I sleep better,” must wait months for approval and keep his gun at home at all times.

His purchase options are also limited: the largest weapons in Mexico’s single gun store — including semiautomatic rifles like the one used in the Aurora attack — can be bought only by members of the police or the military. Handgun permits for home protection allow only for the purchase of calibers no greater than .38, so the most exotic option in the pistol case here consisted of a Smith & Wesson revolver selling for $803.05.

Mr. Vargas, like some other customers, said the rules were a tad overbearing. “It’s too hard to get a gun here,” he said. But he added, “In the United States, it’s far too easy.”

Many Mexicans acknowledge that Mexican violence would not disappear even if American laws were more restrictive. “If the criminals didn’t get their guns from the U.S., they would just get them from somewhere else,” said Mr. García, the gun club member.