Legendary gun designer Eugene Stoner invented the AR15 and redefined the modern rifle.

Decades later with his friend and business associate C. Reed Knight Jr., Stoner offered up an improved version of the AR15, the Knight’s Armament Company SR-15. The re-design was among the last guns Stoner worked on before his death in 1997 at the age of 74 with nearly 100 patents to his name.

At first glance, Stoner and Knight seemed like an unorthodox pair, but their combined visions aligned to create one of the most powerful gun designing duos in history, brought together by a phone call by Knight after learning the two men lived near each other in Florida.

The Knight’s Armament Company SR-15 stands for Stoner Rifle for gun designer Eugene Stoner. This SR-15 M4 Carbine is chambered in 5.56mm with a 16-inch barrel. It was sold by Rock Island Auction Company in April 2013 for $2,875.

Eugene Stoner before the SR-15

Stoner was born in Indiana in 1922. He went to work as an armament installer for Vega Aircraft after high school and before enlisting in the U.S. Marine Corps during World War 2. As a Marine, he served in the Pacific Theater as an aviation ordnance specialist.

After the war, Stoner worked for aircraft manufacturer Whittaker. There he met the chief machinist and began tinkering with gun ideas. He designed the Model 5, one of his first guns, utilizing aircraft grade aluminum. He was pulled away by Armalite, and his new employer turned to making auto-loading firearms.

Despite not being adopted by the U.S. Military, the AR10 was used by Sudan and Portugal, as well as the French Foreign Legion. This rifle was sold by RIAC in September 2021 for $37,375.

Developed in the early 1950s, Stoner’s AR10A showed hints of what was to come, with its aircraft grade aluminum receiver, a direct impingement gas system, a flash hider/compensator, carry handle sights and a steel-lined aluminum barrel. A Springfield Armory design was selected over the AR10 and adopted as the M14 rifle in 1958.

The M14 was heavy but had recoil to match, making it difficult to control when fired full auto. The military went back to the drawing board, but Armalite got there first. The military considered a small caliber, high capacity round but found it weak, eventually leading to the .223 Remington or the 5.56mm cartridge. Design changes like moving the charging handle to the back of the receiver to prevent excessive heating were made and the U.S. Army adopted the Armalite gun as the M16 in 1963.

This M14 manufactured by Harrington & Richardson about 1962-63 on a government contract had a brief military career. It was also used by the Border patrol and National Park Service. This rifle, sold by Rock Island Auction Company in May 2022 for $76,375, was in the inventory of the Department of Energy.

Armalite didn’t have the resources to produce the new M16 in the numbers needed, so the company sold the design to Colt. Also, the Army started tinkering, changing the cartridge powder load so it was more corrosive, creating higher pressure and more susceptible to jamming. The gun was pushed by the military as self-cleaning, but these new changes caused jamming on the battlefield. Minor modifications were made and the M16A1 went on to a long service life with the U.S. military.

This highly desirable Colt/Armalite AR15 Model is select fire and was reportedly in the very first contract run in 1960-62 and is a wonderful example of of an original with green plastic handguards, buttstock and pistol grip. It sold at RIAC May 2025 Premier for $94,000.

Stoner left Armalite to serve as a consultant to Colt and then worked for Cadillac Gage where he designed the Stoner 63 weapons system in the early 1960s. A modular system, the Stoner 63 could serve a number of purposes through its 15 sub-assemblies, depending on how it was configured, like an automatic rifle, light machine gun or squad automatic weapon.

About 4,000 were manufactured and some saw action during the Vietnam War. The Stoner 63 was well-liked by special operations units though the gun didn’t do well on extended missions because of its complexity and tolerances that couldn’t handle the dirt and muck of the jungle. It was retired in 1983. Stoner left Cadillac Gage to found ARES Incorporated in 1971.

This Stoner 63 modular machine gun was among about 4,000 made between 1964 and 1971 at the Cadillac Gage plant in Warren, Mich., and is one of only five believed to be transferable. A number of accessories were included in this belt-fed Stoner 63 when it sold at Rock Island Auction Company’s May 2025 Premier Auction for $411,250, a new world record for the Stoner 63.

KAC before the SR-15

Knight, an entrepreneur who will turn 80 later this year, worked numerous jobs and created several businesses before his namesake company. Growing up in Florida, his family owned a citrus farm, but Knight also ran a refuse business and a police supply store. He raced cars and repaired guns before founding Knight’s Armament. A born tinkerer who grew up rebuilding and modifying cars, one of his early side hustles was to repair Stoner 63 rifles for the Navy SEALs. He also sold the military its first Beretta 92 pistols.

He bought his first Stoner 63 in the rifle configuration for $1,700 in 1974. In his travels, Knight learned parts for the Stoner 63 were hard to acquire, but also that Stoner lived in Florida nearby. He called and found out that Stoner had a warehouse full of parts in Ohio. A business arrangement in the late 1970s led to a friendship between Stoner and Knight. Knight founded his own business, Knight’s Armament Co. in 1982. Stoner came aboard in 1990.

This Light Weight Military Match variant of the Knight’s Armament SR25 sold for $22,325 in Rock Island Auction Company’s May 2025 Premier Auction.

An early Knight product was suppressors for the Navy as well as hand rails for mounting accessories to military firearms. In an interview with Small Arms Review, Knight mentioned that Stoner’s original gun didn’t have such a rail and he said something to his friend.

As the story from Knight goes, he said: “Why in the world didn’t you give me a place on this M16 that was square to the bore, so that I can mount something on that would always be parallel to the bore?” (Stoner) said, “Well, what is it that you wanted me to mount? What is it that you have in mind that you’re going to mount to this?” I said, “Well, like maybe a laser,” and he looked at me and he said, “Yeah, in 1958 I was thinking about a laser.”

SR-15: Redesigning the AR15

When Stoner arrived at Knight’s Armament, he had years and years of field notes on the AR15. “I at one time or another I tried to get back in and make some contribution you know to the weapon,” Stoner has said. “And it turned out to be rather a fruitless thing I was told.

“For instance: I wanted at one time, due to some field problems they had, to go in and I suggested to the Army in how to make the weapon a little better and particularly in corrosion resistant materials.”

Stoner ran up against bureaucratic cost effectiveness and told them he couldn’t offer any more assistance. At Knight's, the KAC SR-15 was an opportunity for Stoner to right some of the wrongs he saw in the AR15.

A closeup of the receiver of a KAC SR-15.

The SR-15’s bolt is the most obvious difference, made with a larger bolt face and rounded locking lugs to lock smoother and resist breaking. The extractor has a dual spring system for better gripping the cartridge case and the proprietary barrel and gas system is a straight line and sealed. This was different from the gas impingement system that fouled the M16 due to the military’s changes in the 1960s.

The SR-15 features an ambidextrous bolt catch and selector switch on the lower receiver. It has a muzzle device for mounting a suppressor and a top-mounted barrel rail. Reviewers have described the gun as an accurate and durable shooter with a smooth two-stage trigger. Some may be put off by the gun’s proprietary parts, its price and scarcity.

“It’s a 5.56x45mm rifle that uses a gas impingement system, M16 family, and we improved many things that we think makes it a superior, reliable weapon,” Knight told Small Arms Review.

A closeup of the muzzle of the SR-15 with its flash hider that also serves as a mount for a suppressor.

Stoner didn’t just tinker with his modified SR-15 design, he also created the SR25, a designated marksman rifle based on his earlier AR10 design. The gun received its name by adding the numbers of the AR10 and AR15. United States Special Operations Command adopted the SR25 as the Mk 11 MOD 0 in May 2000 after a change in barrel length from 24 inches to 20 inches. It was used by U.S. Navy, Marine Corps and Special Forces units during the Global War on Terror before they were retired in 2017.

A different view of the SR-15 receiver.

Eugene Stoner’s Gun: SR-15

One of the most influential gun designers of the 20th century, Eugene Stoner invented the modern rifle with the AR15 for Armalite. Decades later he took on a redesign for Knight’s Armament to make an already reliable gun even more so, adding the SR-15 to a family tree that includes the M16, Stoner 63 and M110 for the U.S. military.

Examples of the SR-15 and Eugene Stoner's other firearms can be found in upcoming Rock Island Auction Company auction events, where hundreds of new guns are offered every few weeks.

A final glimpse of the M16. Manufactured in the 1970s and 1980s in the 9 million serial number range, these were built to military specifications for commercial sale. This gun sold earlier this month in Rock island Auction’s Premier Auction realized $49,938.

Sources:

Interview with C. Reed Knight Jr., Part 1 and Part 2, Small Arms Review

Eugene M. Stoner Designs and Guns Before the M16, C. Reed Knight Jr. from American Society of Arms Collectors