NEW ORLEANS - Bullet-makers are working round the clock, seven days a week, and still can't keep up with the nation's demand for ammunition.

Shooting ranges, gun dealers, and bullet manufacturers say they have never seen such shortages.

Bullets, especially for handguns, have been scarce for months because gun enthusiasts are stocking up on ammo.

The rush to buy up ammunition has been attributed in part to fears among gun owners that the Obama administration and the Democratic-controlled Congress will pass antigun legislation - even though nothing has been proposed and the president last month signed a law allowing people to carry loaded guns into national parks.

Gun sales spiked when it became clear Obama would be elected a year ago, and purchases continued to rise in his first few months in office.

The FBI's National Instant Criminal Background Check System reported that 6.1 million background checks for gun sales were issued from January to May, an increase of 25.6 percent from the same period the year before.

"That is going to cause an upswing in ammunition sales," said Larry Keane, senior vice president of the National Shooting Sports Foundation, a trade association representing 5,000 members. "Without bullets a gun is just a paperweight."

"We are working overtime and still can't keep up with the demand," said Al Russo, spokesman for North Carolina-based Remington Arms Co., which makes bullets for rifles, handguns, and shotguns. "We've had to add a fourth shift and go 24/7. It's a phenomenon that I have not seen before in my 30 years in the business."

Americans usually buy about seven billion rounds of ammunition a year, according to the National Rifle Association. In the last year, that figure has jumped to about nine billion rounds, NRA spokeswoman Vickie Cieplak said.

Jason Gregory, who manages Gretna Gun Works just outside New Orleans, has been building his personal supply of ammunition for months. His goal is to have at least 1,000 rounds for each of his 25 weapons.

"I call it the Obama effect," said Gregory, 37, of Terrytown, La. "It always happens when the Democrats get in office. It happened with Clinton, and Obama is even stronger for gun control. Ammunition will be the first step, so I'm stocking up while I can."

So far, neither the new administration nor Congress has been markedly antigun. Obama has said he respects Second Amendment rights but favors "common sense" on gun laws. Still, worries about what could happen persist.

Demand has been so heavy at some Wal-Mart stores that a limit has been imposed on the amount of ammo that customers can buy. The cutoff varies according to caliber and store location, but sometimes as little as one box - or 50 bullets - is allowed.

At Barnwood Arms in Ripon, Calif., sales manager Dallas Jett said some of the shortages had leveled off, but .45-caliber rounds are still hard to find.

"We've been in business for 32 years," Jett said, "and I've been here for 10 and we've never seen anything like it."

Nationwide, distributors are scrambling to fill orders from retailers.

"We used to be able to order 50 or 60 cases and get them in three or four days easy; it was never an issue," said Vic Grechniw of Florida Ammo Traders, a distributor in Tampa, Fla. "Now you are really lucky if you can get one case a month. It just isn't there, because the demand is way up."

A case contains 500 or 1,000 bullets.