Ammunition and semiautomatic rifles flew off the shelves of gun stores. Second Amendment groups welcomed a flurry of new members. Dave Trahan, the executive director of the Sportsman’s Alliance of Maine, said the group’s membership had grown 120 percent over the last year, gaining 70 to 100 new members each month. The alliance, he pledged, would fight any attempt to place an initiative for background checks on the state ballot.

But even some staunch supporters of gun rights concede that advocates of stronger legislation have won some striking victories.

“I think the Bloomberg side made very significant progress in some states,” said Dave Kopel, a lawyer and the Second Amendment project director at the Independence Institute, a research group.

“When you look at the state scoreboard,” Mr. Kopel said, “they’re roughly in a position of parity this year, which is doing well for them.”

Since the Newtown shooting, robust background check laws or packages of gun legislation were enacted in four states with Democrat-controlled governments — Connecticut, Delaware, Maryland and New York — as well as in Colorado, the site of two mass shootings, in Aurora in 2012 and in Columbine in 1999.

Others states, including Alabama, South Carolina, Texas and Utah, enacted far more modest legislation to strengthen restrictions on the possession of guns by people with mental illnesses or those involved in domestic violence cases.

Supporters of tightening firearm restrictions also count as a victory the confirmation in July of B. Todd Jones as director of the Bureau of Alcohol, Tobacco, Firearms and Explosives, an agency that had been leaderless for six years. And they argue that the tide of new laws weakening existing gun laws has been slowed in the aftermath of the shooting in Newtown.