Anyone familiar with gun collecting knows that this pursuit has its fair share of so-called “unicorns.” The Colt Monitor is one such rarity, a gun so scarce that even Rock Island Auction Company has only offered a single example.

For Rock Island Auction Company, it’s always unicorn season, and the Colt Model R80 Monitor Machine Rifle fits that label to a tee. This example sold in RIAC's December 2018 Premier Auction for $115,000.

Rock Island Auction Company's frequent slate of auctions feature some of the rarest machine guns available to the collecting public. In addition to the elusive Colt Monitor Machine Rifle, we've offered several exceptional examples of the Stoner 63, the FG42, the StG-44, and the crown jewel of the genre, the M240 platform.

An M240B general purpose medium machine gun achieved $470,000 in RIAC's May 2025 Premier Auction.

The Roots of the Colt Monitor

The development of the Colt Monitor began in February 1917, when John Moses Browning (inventor of the famed Model 1911 pistol) presented two automatic weapon designs to officials in Washington D.C. By this time, the First World War had been raging for three years. Even as a bystander, the US military understood how instrumental automatic weapons had become on the modern battlefield.

This initial live-fire presentation of Browning's automatic designs took place in front of a crowd of around 300 people, many of which were high-ranking military and government officials. Much of the crowd was highly impressed with both Browning's water-cooled machine gun and his shoulder-fired offering, the latter dubbed the BMR or Browning Machine Rifle.

This Browning Automatic Rifle made by Colt realized a price of $57,500 in RIAC's December 2021 auction.

Both designs were tested further at Springfield Armory in May 1917 and were unanimously recommended for adoption. The liquid cooled, belt-fed offering would become known as the M1917. To avoid confusion, the shoulder-fired machine gun was designated the M1918 Browning Automatic Rifle, or "BAR."

In July 1917, Colt was contracted to supply 12,000 BARs to the military. With America gearing up for war and straining to supply its allies, Colt already had its hands full trying to deliver previously existing contracts and requested a delay to expand their facilities to accommodate BAR production.

This outstanding U.S. Winchester Model 1918 Browning Automatic Rifle sold for $105,750 in RIAC's May 2023 Premier Auction.

The government next approached Winchester Repeating Arms Company, who helped refine the M1918. One of the major changes implemented by Winchester was moving the ejection port to the side rather than on top. The initial contract with Winchester was for 25,000 of the Browning Automatic Rifles, and by June 1918 they were in full production.

Shortly after, both Colt and Marlin-Rockwell Corp. also began production of the M1918. By the time the First World War ended on 11 November 1918, 52,000 Browning Automatic Rifles had been delivered between the three companies.

Though relatively few BARs saw service on the front, their value was evident. For example, after witnessing the Browning Automatic Rifle in auction during the Meuse-Argonne campaign, the French ordered 15,000 to replace their own light machine guns.

Post-war military downsizing and reduced urgency to modernize armaments after the "war to end all wars" resulted in far fewer military contracts. Colt, who had received the patents and full manufacturing rights for the M1918, began to seek other markets for the weapon. The "Colt Automatic Machine Rifle Model 1919" variant was designed for the general public, and several more civilian and law enforcement-focused iterations of the platform would follow, including the eventual Monitor.

The R80 Colt Monitor Machine Rifle (top) compared to the R75A (bottom.)

The Colt Monitor Machine Rifle

Colt's commercial versions of the BAR were made up of mostly overrun M1918 parts. Due to their limited civilian usefulness and high price point, these iterations of the weapon didn't sell well, but they did lead to a military version designated the R75 in 1925. A law enforcement increment of the R75 offered in 1931 would become known as the R80 or Colt Monitor.

An early example of the Colt Monitor Machine Rifle, serial number C-103110.

The R75 was an improved version of the M1918, having a pistol grip and dust covers added, but they didn’t see widespread orders. The R80 Monitor that followed was intended to be a lightened, shoulder fired version for law enforcement to counter the rampant and heavily armed crime organizations that were plaguing the country at the time.

Special Agent John W. Core fires the Colt Monitor.

Like most R80 Colt Monitor rifles, the example below displays the following markings on the top of the receiver: "COLT AUTOMATIC MACHINE RIFLE/MODEL R 80 CAL. .30/BROWNING PAT FEB. 4. 1919/APR. 14. 1925, AUG. 4. 1925/COLTS PAT FIREARMS MFG. CO./HARTFORD, CONN. USA”. The raised area behind the ejection port is marked “COLT/MONITOR”.

The Colt Monitor Machine Rifle would go on to be designated the FBI’s "Official Fighting Rifle."

The Monitor: The FBI's Official Fighting Rifle

Many police departments had already acquired Thompson submachine guns to supplement their firepower in countering these powerful gangs, but even the venerable .45 ACP often struggled against the thick vehicle doors of the era. Law enforcement sought something with more penetrating power that could stop these gangsters in their tracks, and Colt seemed to have just the solution with the Monitor design.

The Colt Monitor Machine Rifle's .30-06 chambering offered more firepower against steel paneled vehicles than the .45 ACP Tommy Gun.

The R80 Colt Monitor got its barrel shortened to 18 inches and lightened, the dust covers were removed, the pistol grip of the R75 retained, the bipod removed, and a large Cutts style compensator was added to help manage the significant recoil of the .30-06 cartridge.

A closer look at the unique muzzle break/flash hider found on this Colt R80 Monitor machine gun that sold in 2018 at Rock Island Auction Company.

From surviving documents, it appears that Colt first approached the FBI about the Monitor Machine Rifle in June 1933. Due to the rampant organized crime of the time, J. Edgar Hoover and the FBI placed an order for 90 of the R80 Colt Monitors the following summer, which were to be issued to various agents across the country. This would be the largest order and issuance of the machine gun during its production, though perhaps not the most famous.

23 of the 86 initial Colt Monitors had been delivered to the FBI by June 7, 1934 according to Assistant Director W. R. Glavin.

Hunting Bonnie and Clyde

Some of the most famous use of the M1918 and Colt Monitor during the organized crime era revolves around the notorious bank robbers, Bonnie Parker and Clyde Barrow. An M1918 stolen from a National Guard armory in Enid, Oklahoma was known to be Barrow’s weapon of choice and he also taught Bonnie to use it skillfully.

A documented Winchester Model 1895 lever action rifle that belonged to Public Enemy No. 1 and member of Bonnie and Clyde's Barrow Gang, Floyd Hamilton sold at Rock Island Auction Company in May 2024 for $17,625.

In 1933 near Platte City, Missouri, Bonnie and Clyde and their accomplices were nearly cornered by a group of police officers, many of whom were armed with Thompson machine guns and an armored car. Barrow unleashed his M1918 on the officers and a bullet managed to cause the horn of the armored car to malfunction, which many of the officers believed to be a ceasefire signal, allowing the gang to escape.

In a shootout near Sowers, Texas in September 1933 the couple were ambushed by deputies, one of which was armed with a BAR. During the ambush, a round from this weapon managed to pass through the car, as well as both Bonnie and Clyde’s legs, proving the capabilities of the weapon in countering organized crime and "armored" vehicles.

In 1934, the retired Texas Ranger Frank Hamer was called upon to track down and finish the Barrow gang. Sources aren’t entirely clear how exactly Hamer came into possession of a Colt Monitor, but it appears that it came directly from Colt. Some sources say that Colt sent it to him personally, which isn’t hard to believe considering the high-profile nature of the hunt for Bonnie and Clyde. Others suggest that Hamer ordered the weapon from Colt himself.

It is believed that Hamer’s Monitor was serial number C-103168, which now resides in the Texas Rangers Museum. Regardless of how it was acquired, there was a Colt Monitor as well as multiple M1918s present on the day when Bonnie and Clyde's trail of terror came to an end.

Two of the guns used to take down Bonnie and Cylde (Top) Colt Monitor serial number C-103168. (Bottom) A Remington Model 8 self-loading rifle in .35 Rem.

In May of 1934, after being separated from the rest of their gang, Bonnie and Clyde were lured to a rural road in Bienville Parish, Louisiana where Frank Hamer, Maney Gault, and a four-man posse of law enforcement officers laid an ambush. The officers were armed to the teeth and had convinced a relative of one of the gang members to park his truck on the road as if he was changing a tire while the posse lurked in the brush.

At around 9 am on 23 May, Parker and Barrow came racing down the road in their Ford V8. According to a statement by Officers Hinton and Alcorn after the fact, each of the posse was armed with an automatic rifle, a shotgun, and various handguns. It was the automatic rifles which they opened up with first, riddling the two gangsters with bullets before they had even stopped the car. Many sources believe that Hamer had given the Colt Monitor to Officer Hinton to use during the ambush, though this can’t be confirmed.

Bonnie and Clyde carried an arsenal of firepower, including a modified BAR.

In the 2019 movie 'The Highwaymen,' it is Gault (Woody Harrelson) who can be seen prominently using the Monitor during the ambush, while Hinton (Thomas Man) uses a military pattern M1918. Regardless of who was pulling the trigger, the impressive firepower of the Colt Monitor and the M1918 had helped bring an end to the gangsters.

Interestingly, at least two BARs were also recovered from the bullet-ridden vehicle after the shootout. Both of these BARs had been cut down and modified in very similar ways to how the Monitor came from the Colt factory.

A BAR magazine and five .30-06 Springfield cartridges attributed as recovered from the Bonnie and Clyde "death car" sold at Rock Island Auction Company in May 2024 for $18,800.

The Colt Monitor in Pop Culture

As mentioned, the hunt for Bonnie and Clyde has been most recently depicted in the movie 'The Highwaymen' starring Kevin Costner and Woody Harrelson. Other notable appearances of the Colt Monitor include the 2013 'Bonnie and Clyde' miniseries and 'Last Man Standing' from 1996, a Prohibition-era Bruce Willis action vehicle. In the 1967 'Bonnie and Clyde,' the Tommy gun, one of Hollywood's favorite firearm models, is used instead of the BAR or the Monitor.

Kevin Costner fires the Colt Monitor in 'The Highwaymen.'

While the Colt Monitor's rarity has made it a popular firearm among gun enthusiasts, it's seen little coverage in the video game world. In the 'Call of Duty,' 'Medal of Honor,' and 'Battlefield' series, the BAR makes frequent appearances, as well as being featured in 'L.A. Noire.' Recently, 'Enlisted: Invasion of Normandy' from Gaijin Entertainment offers a squad equipped with the Colt Monitor.

In 'Enlisted: Invasion of Normandy,' the Colt Monitor is described as "a modified version of the Browning M1918 with a compensator and reduced recoil."

Colt Monitor Machine For Sale Today

The high cost of the Colt Monitor, nearly $6,000 at the time when adjusted for 2025 inflation, contributed to its scarce production run. Colt's limited marketing was another factor. Of the mere 125 Colt Monitor Machine Rifles produced, 90 were sold to the FBI, 11 to the US Treasury Department, and the rest were purchased by police departments, prisons, and security agencies, making it one of the most sought-after unicorns in all of arms collecting.

This exceptionally rare early original Colt Model R80 Monitor fully automatic machine gun sold in December of 2018 at Rock Island Auction Company for $115,000.

Machine gun prices are on the rise across the board, so it's little surprise that a rarity like the Colt Monitor commands such a hefty sum on the auction block. In Rock Island Auction Company's December 2018 Premier Firearms Auction, a Colt Model R80 Monitor broke the six-figure barrier and sold for $115,000. Today, such a scarce offering would likely realize an even higher price, and like other unicorn collectibles, its potential to appreciate in value makes the Monitor all the more desirable.

Find the rarest machine guns for sale at Rock Island Auction Company.

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This Cadillac Gage Stoner 63 modular belt fed machine gun sold at Rock Island Auction Company in May 2025 for $411,250, shattering the world record.

Sources:

Ballou, James L. (2000). Rock in a Hard Place: The Browning Automatic Rifle.

https://www.forgottenweapons.com/colt-monitor-the-first-official-fbi-fighting-rifle/

https://www.breachbangclear.com/colt-monitor/

https://www.guns.com/news/2019/05/24/full-auto-friday-colt-monitor-edition-videos