Twisted into a rage by his crumbling marriage, 35-year-old Albert Petrosky walked into a Colorado grocery store four years ago and gunned down his wife. Then he stationed himself on a slope outside, waiting for police. When Jefferson County Sheriff's Sgt. Timothy Mossbrucker pulled up in his cruiser, Petrosky killed him in a blast of gunfire.

Investigators were stunned when they saw one of Petrosky's weapons: a .50-caliber sniper rifle. When the gun was test-fired, a bullet bore through a manhole cover "like a hot knife through butter," said Jefferson County Chief Deputy District Attorney Peter Weir. "It's probably the most powerful weapon I've seen in 20 years of prosecuting cases."

That power horrifies gun control advocates but enthralls gun lovers, who have elevated the .50-caliber weapon -- the largest sniper rifle available to civilians -- to iconic status within the growing subculture of firepower enthusiasts. Exalted in gun magazines, sold on the Internet and adored by competitive marksmen, sniper rifles are creating their own niche in the firearms market.

And a backlash.

"How is it this could be available in the civilian market?" asked Rep. Rod R. Blagojevich (D-Ill.), who has proposed banning the gun. "It is designed to take out armored personnel carriers, fortified bunkers, helicopters."

Indeed, Barrett Firearms Manufacturing Inc. markets its popular semiautomatic M82A1 by boasting that it is the most widely used .50-caliber rifle among armies around the world. Ads cite its "battle-proven performance" and success in detonating land mines from a distance.

The cost of the rifles (often more than $6,000) along with their powerful recoil and unwieldy size (some weigh more than 100 pounds and all are more than five feet long) might deter many criminals. But not rich drug dealers or determined terrorists.

The .50-caliber rifle's long-distance capacity makes it ideal for an assassination attempt. When it was introduced to the civilian market in the early 1980s, the Secret Service argued unsuccessfully that it should be outlawed, according to Joe Vince, a former official at the Bureau of Alcohol, Tobacco and Firearms. Today, the rifles can be easier to buy than pistols. Unlike handguns, the rifles are available to buyers as young as 18.

Blagojevich and Sen. Dianne Feinstein (D-Calif.) are preparing legislation that would ban the rifles for all civilians except for competitive marksmen who belong to .50-caliber shooting clubs. In those cases, the guns would be kept under the control of the club itself.

The proposed ban, however, faces serious opposition from an unusual contingent of shooters. Begun in the 1980s by a group of engineers, the .50-Caliber Shooters Association has seen its membership expand to 1,600. And those members have upscale demographics: their average age is 45, nearly half are college-educated and 60 percent earn more than $50,000 annually, according to club files.

The gun's size and power are part of the allure, said James A. Schmidt, an ammunition manufacturer who is on the board of the .50-Caliber Shooters Association.

"There is a fascination with the long range, the larger caliber," he said. "To a lot of these shooters, it's the next level up. It's not any different than if you drove a Cadillac for years, and now you're going to a Mercedes."

In addition to its attraction for marksmen, Schmidt said the gun is also popular among some hunters of elk and moose.

Tom Diaz, who authored a study on the sale of sniper rifles for the Violence Policy Center, argues the gun's allure is manufactured to make more sales in a saturated market.

"The gun industry, by necessity, looks to innovation, which is increased lethality," Diaz said.

Shaped by the Internet, videos and magazines, the weapon acquires a macho romanticism embodied in a sniper slogan: "one shot, one kill."

"Read about the weapon that makes men shiver," states an ad in Guns and Ammo. One catalogue lists a page of sniper posters, T-shirts and books, including "The Ultimate Sniper" and "The Poor Man's Sniper Rifle."

Diaz contends that the glorified image draws a young, impressionable and sometimes unstable audience. But .50-caliber fans argue that the guns are too expensive and heavy to be much of a crime threat.

"This is not a rifle you run down to the gun store and buy," Schmidt said.

Still, the weapons are turning up regularly in criminal conspiracies. The Irish Republican Army used them to snipe at British soldiers. Seven Cuban Americans were indicted in a plot to assassinate Fidel Castro after two of the rifles were found hidden on a boat off the coast of Puerto Rico in 1997.

An investigation by the General Accounting Office's special investigations unit found 17 incidents where suspected criminals had the guns.

Police have found them in the possession of drug dealers in at least three states.

One of the rifles was found at the Branch Davidian compound in Waco, Tex. And one was found last year in an arsenal amassed by John C. Clark, a 48-year-old mentally disturbed man who killed a Traverse City, Mich., police officer.

Traverse City police Det. Derek Sutherin said Clark had tried to haul the rifle to the front door to use against police who had surrounded his house but was hampered by a gunshot wound to his arm.

"If he had got to his .50-caliber, there aren't big enough trees to hide behind," Sutherin said. "That weapon will go through a four-foot tree like it wasn't there."

The .50-caliber evolved from the fearsome Browning machine gun of World War II fame. More modern and accurate than its machine gun ancestor, the first .50-caliber civilian sniper rifle was designed in the early 1980s by Ronnie G. Barrett, owner of Barrett Firearms Manufacturing. Barrett and others now produce both semiautomatic and bolt-action models.

While six companies manufacture .50-caliber rifles, Barrett's M82A1 has drawn the most attention. It was featured in the 1987 movie "Robocop" and used by the U.S. military in the Persian Gulf War to fire armor-piercing shells at tanks, armored personnel carriers and land mines.

Barrett's Web site highlights the company's round-the-clock rush to manufacture 100 M82A1s for Marines fighting in the 1991 Desert Storm war against Iraq. Barrett said he has produced roughly 1,600 of the .50-calibers.

The assault on the gun, he argued, is misdirected because his .50-caliber rifle is only slightly more powerful than a standard elk rifle. It is able to penetrate armored vehicles only when loaded with special ammunition, he said.

He called the .50-calibers "a toy for a big boy."

Blagojevich has also introduced legislation, now before the Judiciary Committee, to limit the sale of armor-piercing and incendiary ammunition for the .50-caliber rifles. Such ammunition is currently banned for handguns but not rifles.

The House recently adopted another Blagojevich amendment prohibiting the U.S. military from selling outdated .50-caliber ammunition. That provision is now before a Senate-House conference committee.

The gun enthusiasts will not go quietly. To Schmidt, it's a matter of letting people pursue their hobbies.

"I don't think it's any different than raising schnauzers or learning how to cook," he said. "People have their fascinations."