NOEL, Mo. -- Seated on a low bench, Jim Spears used a piece of deer horn to whittle down a heavy chunk of Missouri flint. For an hour, he tapped, whacked and smoothed the hard rock until it was transformed into a delicate and potentially deadly artifact: a replica of an Indian arrowhead known as a Dalton point.

"Every stone is different and every stone is a challenge," said Mr. Spears, as he chiseled away and the arrowhead grew thinner and sharper. "It helps me get into the minds of ancient people."

At 62 years old, Mr. Spears is one of the country's finest flint knappers, a breed of die-hards who re-create ancient arrowheads, knives and tools using original Stone Age techniques.

More than 10,000 years ago, prehistoric Americans attached sharpened stone "points" to spears and hunted woolly mammoths. In the 1960s and 1970s, a handful of archeologists made basic, often clumsy arrowheads in order to better understand ancient tool making. Since then, knapping has taken off as a surprisingly popular American pastime and art form.

Hundreds of modern-day Stone Agers now gather at weekend "knap-ins," where they chip rock, swap techniques and trade arrowheads. Novices eager to learn the skill pay $500 or more to attend workshops. Dozens of books and videos -- including one called "Caught Knapping" -- tout the craft. A glossy magazine for knapping devotees, Modern Lithic Artists Journal, launched last year and featured Mr. Spears's work in the first issue. Another quarterly bible of the trade is called Chips.

"It's a manly hobby, because of its association with hunting and weapons," says John Whittaker, an archeologist-knapper at Grinnell College, Grinnell, Iowa. Indeed, some knappers make practical use of their handiwork, hunting deer and other creatures with the carefully honed points.

Prof. Whittaker estimates that there are at least 5,000 knappers in the U.S., mostly men, who churn out 1.5 million pieces a year. Replica arrowheads sell on the Internet for $10 to $100 or more apiece, and are increasingly turning up on eBay. One 5-inch "turkey tail" arrowhead, for instance, recently sold for $202.50 at the site, even though its pedigree was unclear. (The seller said it "looks old.")

Old-time knappers worry about commercialization of their craft. That's because the best knappers have become so skilled that their work can be difficult to distinguish from Stone Age objects. Some archeologists fret that modern arrowheads are more likely now than in the past to be sold as originals, muddying the historical record. Other purists, such as Errett Callahan, who runs workshops on the traditional approach in Lynchburg, Va., contend that some of today's "wild, modernistic" designs make a mockery of an ancient skill.

While newer hobbyists sometimes rely on copper implements -- which most Stone Age people never had -- Mr. Spears insists on doing things the old, old way. A resident of Noel, Mo., he has knapped steadily for four decades. He gathers flint near his home in the Ozarks. He only uses tools available to prehistoric Americans, including bison rib and deer horn, which he obtains from hunts or at a butcher's shop. Even with these crude implements, arrowheads can be carved to be sharper than surgical scalpels.

When practicing his craft, Mr. Spears folds a piece of buckskin over his left leg and uses his thigh as an anvil. He holds the stone in his left hand and hits it with a piece of animal horn known as a billet. By delicately adjusting the pressure of his fingers under the rock, he is able to channel the force of the blow along natural lines in the stone, knocking off flakes exactly where he wants. A single wrong strike can ruin a piece. But Mr. Spears intimately understands the physics of percussion.

"He can do things to a rock that are miraculous," says Bob "BigFlint" Hunt, a knapper from Oak Grove, Mo., who has known Mr. Spears for more than two decades. Another colleague recalls that at a small 1993 gathering, everyone dropped their tools to watch Mr. Spears chisel a complicated turkey tail arrowhead.

After spending four years in the Navy, Mr. Spears did a brief stint at junior college. While there, he saw a friend craft an arrowhead by flaking a piece of flint with a beer opener. In a book for Boy Scouts, Mr. Spears read that prehistoric Americans had used deer horn to chisel points; he decided to do the same. "I was enthralled by the idea," he says. "I began to chip all the time."

One day, as he crouched on a rocky bluff hitting a stone, a man pulled over in his car and shouted: "Hey, what you doing there?"

"Making arrowheads," Mr. Spears answered back. The man paused, then shook his head and drove off. "Guess he thought I was nuts," says the knapper.

Over the years, Mr. Spears taught himself to knap increasingly intricate designs such as the exquisitely fluted "Folsom point." Eventually, his lifestyle began to reflect his obsession. He took to hunting deer with a bow and arrow. He sometimes sat around a fire and skinned carcasses with stone implements he had made.

Mr. Spears's large house in the middle of the Ozark hills is bare, except for a few Indian rugs and a mattress on the floor. Though he has an old telephone -- which he's been known to unplug -- he doesn't own a wristwatch. In one room he stores 40 large pieces of bamboo, from which he carves bows and arrows. He has never married. His longtime girlfriend, who is part Native American, lives several miles away.

It's hard to make a living from knapping alone. Mr. Spears, who used to dabble in construction work before taking up his craft full-time, says the Internet has lately damped his arrowhead sales. So he also trades other Native American products through a friend, Diana Benson. Her mail-order knapping supply firm sells Mr. Spears's arrowheads, as well as rugs and baskets, on the Internet. The shelves of her Missouri Trading Company store, in Pineville, Mo., are heaped with rocks, tools and about 30 instructional video titles -- including one starring Mr. Spears.

Mr. Spears attends about four knap-ins each year. One recent weekend, he stowed his tools and workbench in his pickup, and drove 250 miles north to the Fort Osage knap-in, held in a field in northern Missouri. Along the way, he snacked on dried fruits and deer jerky made from an animal he had killed.

At the event, more than 100 knappers from Iowa, Illinois, Texas and elsewhere, sat in circles and, for hours, whacked away at rocks. Most were middle-aged men -- carpenters, jewelry makers and at least one professional archaeologist. At one tent, a vendor from Leavenworth, Ind., hawked 1,800 pounds of stone, including jasper and chert. Another attendee described how he felled a deer using an arrow tipped with a stone point.

Mr. Spears didn't even take out his tools. Fellow knappers said they were already in awe of his skill and that he had little to prove anymore. When one collector proudly noted that certain arrowheads could fetch hefty prices, Mr. Spears was bemused. "When you get right down to it," he said, "it's nothing but rocks."