The AR-15 might have stolen the limelight among contemporary rifles, but behind the stage, its lesser-known cousin—the AR-18—was secretly sowing the seeds of a revolution of firearms.
Though it never gained mainstream popularity, the AR-18’s short-stroke gas piston mechanism, small configuration, and adaptable design were the building blocks for some of the world’s most sophisticated military rifles. It began life as a commercial failure and became a mechanical template shared by armies around the world.
The following is a glance at six rifles that bear the AR-18’s DNA, demonstrating that this “forgotten” firearm has left a legacy a lot larger than its sales numbers indicate.
6. SIG MCX Series
Consider the SIG MCX to be a middle ground between traditional design and contemporary innovation. It combines the AR-18’s piston-operated reliability with the ergonomically familiar AR-15, resulting in a platform that is comforting yet brutally capable.
From the MCX Spear—embraced by the U.S. Army as the M7—to the extreme-compact Rattler, this branch of rifles lives on flexibility. Suppressors? Short barrels? Full auto fire? No issue—the piston system accommodates them all while minimizing gas blowback and keeping the action cold. It’s little wonder that premier units ranging from SOCOM to Ukraine’s SBU Alpha Group have adopted it as their go-to gun.
5. CZ-805 Bren
The Czech-manufactured Bren adopts the AR-18’s mechanical soul and encases it in a very modular, contemporary package. In its third iteration, the Bren is easily reconfigured for varying calibers and mission configurations.
That adaptability has earned it favor from units such as the Czech Army, Hungary’s military, and France’s GIGN. Behind its streamlined look is the same piston-driven ruggedness that made the AR-18 so lasting.
4. HK416
If there’s one rifle that most demonstrates the enduring legacy of the AR-18, it is the HK416. Heckler & Koch combined the AR-15 controls with the AR-18’s piston action to create a rifle that’s accurate, reliable, and simple to maintain—no matter the hostile conditions.
Deployed by special troops and taken up by the United States Marine Corps as the M27 Infantry Automatic Rifle, HK416 is best with suppressors and short barrels—much like the AR-18 used to be.
3. FN SCAR
Few rifles are more versatile than the FN SCAR. Available in both 5.56 and 7.62, with detachable quick-change barrels and accessory rails, it can be configured for nearly any mission. This type of modularity is directly from the AR-18’s playbook. Its piston design makes it clean and cool even when run hard, so it has earned the favor of SOCOM, the armed forces of Belgium, as well as Germany’s elite GSG 9.
2. FN F2000
The FN F2000 uses the AR-18’s piston system and puts it within a bullpup layout, creating a short, futuristic carbine that doesn’t compromise barrel length.
With the action behind the trigger, it’s extremely agile—perfect for close-quarters work. Armies in Ukraine, Slovenia, and Pakistan have all used it, demonstrating that the AR-18’s fundamental design suits alternative configurations.
1. Steyr AUG
One of the earliest and most famous users of the AR-18’s piston configuration, the Steyr AUG established the benchmark for the modern bullpup rifle. Its bolt carrier and gas system trace directly to the AR-18, packaged in a unique design that has been used by military and police units since the late 1970s.
Its modularity, reliability, and unmistakable profile have seen it serve for decades, with upgrades keeping it current to the present day.
Why the AR-18 Still Matters
When it came out, the AR-18 short-stroke piston design was prescient. By isolating hot gases from the bolt, it operated cleaner, remained cooler, and provided improved reliability—particularly in suppressed or short-barreled configurations. Its foldable stock provisions and field stripping ease made it ideally suited to contemporary combat requirements.
Though it never became a commercial hit, the AR-18 earned the nickname “the American AK” for its simplicity, toughness, and adaptability. Look beyond the AK-47 and AR-15 families, and you’ll find its engineering fingerprints on nearly every modern service rifle.
The irony? A rifle that history almost overlooked has been quietly shaping the battlefield for over fifty years.