Having spent a month arguing with no end in sight, Charles Gaines and Hayes Noel decided to resolve their conflict the old-fashioned way. They agreed to a gun duel at 20 paces.

It was the late 1970s and Gaines, a writer and fly fisherman best known for authoring Pumping Iron, a book later turned into a documentary that helped usher Arnold Schwarzenegger to superstardom, had been verbally sparring with his friend Noel about who would be better-equipped as a survivalist. Gaines believed someone with outdoors skills like himself would excel. Noel, a Wall Street stockbroker, thought his urban instincts would prove superior.

After going back and forth like this while vacationing on Martha’s Vineyard in Massachusetts, Gaines returned home to New Hampshire and spotted something in an agricultural catalog. It was the Nel-Spot 007, a gun powered by carbon dioxide (CO2) gas and used to mark trees or cattle using a gelatin ball filled with oil-based paint. Gaines thought it would make for an interesting combat simulator. Instead of testing survivalist skills with ammunition, they could test it with globs of paint.

After getting the guns, Gaines and Noel engaged in a duel that Gaines won—this according to Gaines—and also crept around in the woods hoping to snipe the other, a situation which both men later said they had gotten the upper hand in.

These conflicting narratives failed to settle their argument, and so the two friends decided a bigger, more involved experiment was in order. Purely by accident, they created the game of paintball in the process.

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Weapons that shoot projectiles using compressed air are nothing new. In the 1940s, Britain’s commercial freighter ships used steam-powered cannons to launch grenades at enemy aircraft. When they were bored, the sailors used the cannons to shoot potatoes or beer bottles instead. Much later, sports teams would adopt T-shirt cannons powered by the same principle to dispense apparel to fans in the upper decks.

The idea to use CO2 for paint came from the Nelson Paint Company in the 1960s. Hoping to assist foresters with marking trees that weren’t easily accessible on foot, the distributor marketed the Nel-Spot 007, which shot the gelatin balls with a resounding splat. Farmers also used them to indicate cattle that had been bred. (Because the paint was used for marking, the guns were and typically are still called paintball markers, not paintball guns.)

By the time Gaines became aware of the device in 1979 or 1980, it still had no practical use outside of agricultural purposes. Along with Noel and another friend, a ski shop owner named Bob Gurnsey, the trio decided to arrange a combat simulator using the Nel-Spot 007. The duel had proven that being hit with the paintballs resulted in no serious injury. (Gaines reportedly tried it on his wife, Shelby, as well, who reported that “It didn’t hurt much.”) Gurnsey developed a rudimentary set of rules for the competition, which would see the three men and nine other competitors attempt to capture flags from four stations in a 100-acre field in Henniker, New Hampshire, a site not far from Gaines’s home. The object would be to grab the flags and head for a premarked exit without being shot.

In order to maintain the central conceit of their debate, Gaines and Noel tried to recruit a cross-section of personalities for the event. There were outdoorsmen like a forester and Vietnam veteran along with would-be urban tacticians like a trauma surgeon and an investment banker. All were armed with the Nel-Spot 007, goggles, camouflage, paintballs, CO2 cartridges, a compass, and a map.

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The competition was held on June 27, 1981. For two hours, the men stalked around the premises, lurking behind foliage and doing their best to seize the flags without being bombarded by paintballs. Gaines grabbed two flags before getting into a stand-off with a Green Beret, who was holed up in an abandoned woodshed. The trauma surgeon wound up shooting nearly half of the dozen players by himself. But in the end, it was the forester, Ritchie White, who emerged the victor, utilizing a stealth strategy that allowed him to covertly grab all the flags and get out without firing a single shot.

Did the event resolve the debate between Gaines and Noel? Not really. But they were having too much fun to care. So was Bob Jones, a participant and writer for Sports Illustrated who published a story on the competition in 1981. Along with other coverage from TIME and Sports Afield, Gaines, Noel, and Gurnsey were inundated with letters and requests for more information about the rules of the game and the necessary equipment.

Sensing a business opportunity, the three formed the National Survival Game, a business devoted to the burgeoning recreational activity. Gurnsey continued to refine the rules while the others assembled kits consisting of the Nel-Spot 007 and the paintballs. Gaines was able to negotiate a deal with the Nelson Paint Company to license the guns and ammo for non-agricultural purposes.

Soon, they were licensing the National Survival Game brand to franchisees, who opened paintball fields and held organized competitions. By 1982, the National Survival Game was promoting a World Championship, and enthusiasts were modifying the weapons to include pump-action loading, larger magazines, and automatic firing. Because other organizations besides National Survival Game were popping up, the more generic name of paintball was introduced. More importantly, the paint became water-based rather than oil-based for easier clean-up.

While paintball exploded in popularity throughout the 1980s, not everyone was on board. In New Jersey, the guns were considered firearms due to their ability to shoot projectiles at velocity. To acquire a paintball marker, one needed a firearms permit. And even if you had one, you might still leave yourself open to legal problems if you used it to “shoot” at another human being.

The issue wasn’t resolved until 1988, when a paintball enthusiast named Raymond Gong sued the state’s attorney general and Monmouth County prosecutor John Kaye to remove the weapons from the New Jersey Gun Control Act. Judge Alvin Milberg asked for a demonstration and watched as a human target was hit roughly a dozen times without suffering injury. The defense also proved the CO2 cartridge used in a paintball marker was not the equivalent of a cartridge used in a real firearm, a term used to describe ammunition. Gong won and was able to open his own paintball field.

Gaines sold his share in National Survival Game early on, leaving the business to Noel and Gurnsey. The activity has since grown far beyond their initial ambition to settle a friendly debate, with players spending upwards of $169 million annually on equipment. Despite the inherently aggressive nature, it doesn’t seem to be particularly risky, with just 0.2 injuries reported per 1000 participants. While not quite as popular as it was in the early 2000s, there’s still plenty of demand to demonstrate survival skills with one well-aimed paintball.