.50 BMG Flechette rifle

Daniel spotted a very interesting auction at gunbroker.com. The rifle on sale was a Boys Anti- Tank rifle modified by TRW-SYSTEMS GROUP and rechambered for .50 BMG. It was intended to be used for .50 BMG flechette rounds.

 Gb 122223000 122223452 Pix1017941250
Click to expand.

 Gb 122223000 122223452 Pix1017941031

The auctioneer claims that it is only one of twelve built and the only other known example resides at the Ford Benning sniper school.

The .50 BMG Flechette rifle project was contacted out by DARPA in 1960’s. The projectile consisted of a saboted depleted uranium dart weighing 11.9 gram ( 183.6 grains ).

.50 BMG Flechette round cross section. © Paul Smith (Used with permission)

The sabot was fired out of a smoothbore barrel with the dart achieving 4500 feet/sec velocity. That is more than a 32 grain .204 Ruger!

Length Of Projectil
Detailed Drawing © Paul Smith (my modification are in red)

I tried to work out the caliber. Given that 1 cm3 of depleted uranium weights 19.1 grams and the length of the dart is 7.81 cm (I rounded down to 6cm to take into account the spiraling and the point) and then used the formula of a volume of a cylinder:

11.9 / 19.1 = 0.62

sqr(0.62 / ( 6 x pi )) = 0.18 centimeters

[ My math skills not great these days, go easy on me in the comments 😉 ]

A caliber of .07″ is seems some what small. It is impossible to know how much titanium is in the depleted uranium alloy.

Time Magazine wrote about the project back in 1967:

TRW’s magic bullets are unimpressive at first glance. Less than 4 in. long and one-tenth of an inch thick, they resemble the steel flechettes (French for “little arrows”) used in some U.S. antipersonnel weapons in Viet Nam. What the TRW flechettes lack in size, they make up in penetration power. In recent tests, they punched completely through a 2-in.-thick armor plate that would stop most steel flechettes or heavy-caliber bullets fired at it.

Dramatic Travel. It is the uranium that gives the flechettes their impressive muscle. Cleansed of its fissionable isotopes U-235, the depleted uranium is safe to handle. Because it is one of the heaviest natural elements (a 1-ft. cube of uranium weighs 1,167 lbs.), even a tiny uranium flechette fired at high velocity from a gun has so much kinetic energy that it can penetrate a target at an angle as oblique as 60°.

At 0.10 in caliber it would have an incredible ballistic coefficient weighing in at 180 grains! In theory it should be super accurate. In reality it was quite the opposite. It shot 10 shot groups of 6 – 8 feet at 600 yards. That’s over 12 MOA!

TRW was hoping to use the flechette in a rotary gatling / mini gun type system. Daniel writes:

The rifle in the GB [gunbroker] ad looks like the one shown in a photo in Peter Senich’s “The Complete Book of U.S. Sniping”. The photo was credited to Don Stoehr, a former TRW employee.

Among his projects were the Low Maintenance Rifle (LMR) and HIVAP (High Velocity All Purpose) machinegun. The HIVAP was really wild. It was an eight-barrel .31 caliber Gatling based on the Dardick open chamber principle. Like other Dardick-derived open chamber weapons, it used ‘trounds’. The HIVAP trounds used lexan cases loaded with saboted flechette. (However, solid bullet variants intended for testing purposes can be found.) The really wild part was the cyclic rate: just shy of 30,000 rpm. Stoehr later wrote that the twin feeders could support 42,000 rpm and that a switch to electrical priming would allow them to double the existing cyclic rate.

However, I don’t know how they’d ever keep such a monster fed. The weapon pod under design only held either 3,000 or 6,000 trounds.

It is an interesting cartridge that unfortunately will probably never be further developed due to the politics and health concerns of depleted uranium. Carrying DE rounds around would likely be a health hazard to the soldier using them.

More information on the round is available at cartridgecollectors.org.

Many thanks to Daniel E. Watters for information and links and to Paul Smith for the use of his photos.

Steve Johnson

Founder and Dictator-In-Chief of TFB. A passionate gun owner, a shooting enthusiast and totally tacti-uncool. Favorite first date location: any gun range. Steve can be contacted here.


  • Phil

    Is it just me, or should there be some twist on the dart stabilizers? Seems like that would give it more range and accuracy.

  • Tony

    “…and health concerns of depleted uranium.”

    Oh please, not you too? 🙁 The amount of hysteria these days over just about everything is quite depressing. I had higher hopes for such an intelligent blog as this.

    • Tony, lol. Seriously through: would you be happy to carry about radioactive decaying uranium in a pouch on your body? One thing in an aircraft, tank or ship (?) magazine, but another thing on the body. That is asking for trouble.

      Also the chemical produced when DE corrodes can spontaneously combust at room temperature!

  • As for the fins, a former TRW engineer John R. Sellars has written that they did experiment with a slight fin angle. The original fin angle was 1 degree. This was found to add too much drag, adversely effecting the range of the fléchette. Sellars thought that they might be spinning so fast that they were bending the shaft in flight. Later efforts used a 0.5 degree cant. According to Sellars, 20,000 of the .50 BMG DU fléchette round were made.

    FWIW: The prototype HIVAP rounds used steel fléchette. This was probably due to the weapon being a proof of concept model. DU fléchette are a bit much for function testing. You hardly want to contaminate the factory test range, and at ~30,000 rpm, it would get pretty expensive in short order.

    Around the same time, AAI worked on DU fléchette in 7.62mm NATO. The latter had the unfortunate designation DUDS: Depleted Uranium Discarding Sabot.

    I really need to add these to my article on SPIW and fléchette over at The Gun Zone.


  • Woody

    My friend and I were thinking the same thing Phil, twisted stabilizer fins would give the projectile better accuracy but it would slow it down. I don’t know whether it would slow it down to the point where range would be hindered but I bet it would (see murphy’s law: no good deed goes unpunished). Imagine arching the round, if the moa were tighter then you could reach further but again I have no idea what the specs would be. I’m sure they thought about twisting the fins but maybe you can’t effect a spin at speeds approaching mach4, maybe it would time travel, maybe they didn’t actually think of it, who knows? We never will and that makes me sad.

  • jdun1911

    It will destroy any rifling in a matter of a few shots at the speed that the Flechette leaves the bore.

    The fins is more then enough to stabilize the Flechette. The M829A1 is able to gets hit at over one mile.

    • I agree with jdun1911

  • I don’t know about this example, but rifled sabots are typically a soft material that will not wear on the gun’s bore. Besides, this gun must be a smoothbore since the flechette is not designed to spin. (Which would also explain why the flechette load wouldn’t work in a regular .50BMG rifle.)

    Regarding the depleted uranium: It’s no more hazardous to touch than lead. What little radiation it does emit is of a very low energy. A marble floor or granite countertop could pose a greater radiological hazard. Granted, like most other heavy metals it is toxic. You don’t want to breath it or swallow it. Also, at high temperatures (like those created when a supersonic projectile hits a hard target) DU becomes “pyrophoric,” which means it will burn, releasing even more energy at the target.

  • Nomen Nescio
  • Nomen Nescio

    i’m an idiot who shouldn’t be posting so late at night. in addition to forgetting to close that link (i’d meant it to cover only two words…), i went and talked about fission products when i meant to talk about decay products. uranium (even depleted uranium) will spontaneously fission, too, but absent a nuclear reactor that’s such a rare event as to not much matter.

  • DE is pretty innocuous when it’s still riding in your tank’s (or rifle’s?) magazine. The nasty bit comes after it has turned the inside of an enemy APC to burned crispies . . . then you have slightly radioactive, toxic dust left from the round you shot them with. It’s one more thing to worry about (a little) when you are checking a burned out hulk for anything (or anyone) useful in the field

    • Well guys, I stand corrected on the topic of DE and its toxicity

  • Lcpl. Budd

    They’ve got one of these at MCRD (Marine Corps Recruit Depot) San Diego in the museum. It’s .55 caliber, was used in WWII (been almost 1.5 years since I visited the museum, but I’m fairly sure it was WWII) by the British, and was also known as “The Boy’s Gun.”

    No DU (obviously). If memory serves, it was used up to 550 meters in an anti-tank.
    Don’t remember if the total number produced was specified by the museum, but 12 doesn’t sound unreasonable, as the weapon was not widely used.

  • dingebretsen

    I worked on a ARPA program in 1971 that used this round. It was fired from an unmanned QH-50 helicopter (Nellis range 63). I had one of the TRW Boys rifles in my office at Wright-Patterson AFB, until my branch chief made me get rid of it. It was donated to the US Army armament museum at Ft. Aberdeen, MD. I don’t know if it is currently on display there.

    I still have several DU flechettes, and a few spent plastic sabots (they only traveled about 20 ft from the muzzle, and were usually recovered in good condition).

    If this link is still active, I would be happy to answer any questions that anyone has.

    • dwusky

      Hey dingebretsen, I’m a nuclear engineering student and I have quite an interest in DU and it’s properties. Can you possibly email me at coolcarlcool1@gmail.com. Thanks

  • Parabellum

    If you could send me some photos of the spent sabots it would be greatly appreciated, I am currently attempting to modify a single flechette to fire from a 12-gauge and need some insight towards a discarding sabot.


  • Don Schroeder

    In 1971 I flew over a site s.w. of Quan Tre with my indesepensible fighter group in an old DC-3 with three HIVAPs trained on carpeting the ground with fletchets from about 1K feet. ”We discharged about 40.000 round burst in less than 30 seconds, while almost flying sideways due to the cross winds that came up at that time. We were told that the ground forces came through this hamlet soon after we straffed it. Needless to say, they didn’t find anybody alive, pets and livestock included. Then the 101 Airborne dropped several hundred poinds of napalm and high density 500 poiund bombs and the hamlet became a virtual moon surface with not a stick of vegetation.

  • Nater

    The health concerns from depleted uranium are real, they’re just not radiation related. DU is a heavy metal. Heavy metals are very poisonous.

  • Jason

    Actually, while DU can be handled safely, as the radiation is minimal, (making it excellent shielding) breathing in DU dust (produced from the round’s incendiary reaction as it impacts steel armor) is very dangerous. When these particles come in direct contact with lung tissue, the prolonged exposure to alpha radiation will almost certainly cause cancer over time. Unless you never plan to advance on the hardened target this round is designed for, its simply too dangerous to be used as anything except as a weapon of last resort. Even in these cases, targets should be given as wide a berth as possible, and soldiers should never camp in proximity to destroyed targets. By proximity, read as several miles.