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US Special Forces seeking subsonic ammunition for covert missions


November 27, 2012

USAF special forces on a training mission

USAF special forces on a training mission

Most people have experienced the sonic boom of a skillfully wielded whip, or the closely related crack of a nearby bolt of lightning. Such sounds have a character that attracts a good deal of attention, which is why the US Special Operations Command (SOCOM) is trying to silence them. The crack of a rifle shot is the sonic boom of a supersonic bullet, making stealthy ground missions difficult to accomplish. To address this need, SOCOM has issued a Small Business Innovation Research request for proposal for a feasibility study of suitable subsonic rounds.

In dry air at 20° C (68° F), the speed of sound is about 343 meters per second (1,125 feet per second). If a bullet moves faster than that, it generates a sonic boom. SOCOM-fielded rifles with standard combat loads have muzzle velocities of between Mach 2 and Mach 3, which rather suggests that producing a reliable subsonic round may be a difficult task, especially since the rifles in which these will be fired are designed for the upper velocity of which their cartridges are capable.

The rise of urban warfare against individuals and small groups suggests that a source of reliable, accurate, and (most of all) quiet subsonic rounds is, to SOCOM, a highly desirable goal. However, to date, subsonic ammunition performs reliably only in small caliber silenced pistols, which are unsuited to many missions for which subsonic ammunition would be favored, even transformational. Favored, perhaps, but not easily achieved.

Past experience with subsonic rounds reveals significant accuracy problems, which drives a considerable reduction in effective range. Achieving subsonic velocities requires igniting a very small propellant charge in a rather large cartridge, leading to unsteady burning and erratic chamber pressure. Small chamber pressure can lead to gas leakage from the chamber, and also to a greatly increased chance of having a bullet become stuck in the barrel, rendering the rifle inoperable. Such low pressures are also insufficient to reliably cycle the action on current gas-operated semi-automatic and automatic rifles, raising a strong possibility of jamming during use.

It seems clear that new cartridge technologies must be invented to satisfy these conditions. These might include polymer-based cartridges for improved gas sealing, and sabots for sealing of the barrel while insuring predictable barrel friction and highly accurate performance. The feasibility study will produce an outline of the general approach to developing subsonic rounds.

In later phases prototypes will be developed that demonstrate the successful implementation of the new technologies. Assuming funding remains available, a transition from the prototype cartridges and manufacturing methods to full production of the subsonic ammunition designs will be carried out. Dual use by law enforcement is an additional SOCOM goal. Programs to develop military subsonic ammunition have previously been fielded with a consistent lack of success. Perhaps the continuing flow of materials science and manufacturing advances will change the odds this time.

Source: USSOCOM via Wired

About the Author
Brian Dodson From an early age Brian wanted to become a scientist. He did, earning a Ph.D. in physics and embarking on an R&D career which has recently broken the 40th anniversary. What he didn't expect was that along the way he would become a patent agent, a rocket scientist, a gourmet cook, a biotech entrepreneur, an opera tenor and a science writer. All articles by Brian Dodson

Try tiny bullets at much higher speed. That should get them in beneath the human hearing threshold and improve range and accuracy.

Ross Nicholson

I'm curious. Exactly why does any law enforcement officer require sub-sonic ammunition to use against the people it protects and serves?


What about a series of staged ignitions, built into the bullet head, so that the bullet is continuously propelled forward but at a subsonic speed?

Sat Nandlall

Why not just use Silencers ? And there ARE Silencers on Guns other than subsonic hand guns.


Brian Mcc

Flink, nowhere in this article does it mention law enforcement. The article is purely about a military round for Spec Ops use. However, the police could use such a round when doing raids on drug houses, etc. where there are heavily armed potential assailants that could be taken out silently as to not give the other bad guys (victims, as you would probably call them) an audible cue to take up arms. Protect and Serve by taking out or arresting those that do the opposite, i.e. criminals.


Im not sure I understand the problems here, they say the ammo is for urban and close combat environments but then cry about the poor distance performance because of the slower speed? Well which is it? For urban combat for for long range?

Nick Thompson

@ Estelja. Re: Nowhere in this article does it mention law enforcement. The last para of the article states: "Dual use by law enforcement is an additional SOCOM goal."



Last paragraph, third sentence:

"Dual use by law enforcement is an additional SOCOM goal."

US LEO has neither a requirement nor the authority to use anything other than flash suppressors. It's not legal to simply shoot a target unless a hostage or other LEO is about to be shoot by said target. I'm not arguing that it wouldn't make things easier, just that it's not legal.

It's not easy to approach a building unseen nowadays. There are dozens of IR surveillance/security cam systems on the market and they're fairly simple to build from scratch.

Covert entry is seldom practiced in a civilian setting unless there are hostages. Entry into most buildings is accomplished with brute force and plenty of noise. There's no way to do it in silence. At best, you might quietly divert the DWV into a bucket in a crawlspace or capture the outflow to the sewer line before entry so that you don't loose evidence. Once the ram hits the door, there's no need for silence.

Stealth is often practiced but seldom used. It's mainly for building clearing when the environment is mixed (target/friendly) or unknown, and then only when a surreptitious entry is possible. A locked and chained door usually makes that impossible. And it's good practice for the period after the entry if you're working a large, multi-floor building. There are few things that suck more than having someone shooting at you through the floor/ceiling.

UK LEO have access, but only because they have so often had to deal with many flavors of terrorist organizations.


If you want it to be effective at long range and subsonic you have to throw a large heavy bullet (I would recommend some on the order of 60cal.) or have an engine on the bullet. (firing little magnesium or white phosphorous fueled ramjets would be cool.


300 AAC/BLK Does this now with a 220 grain 308 bullet at just over 1000FPS. Works in an M4/AR15 with the swapout of a barrel. Uses standard M4 bolt and magazines. Done


Mark Timon

silencers and suppressors are the same thing. They only mute the sound at the barrel, not the second crack from the supersonic bullet. To be effectively silenced the ammo needs to be subsonic

Will Avent

Subsonic? Does that mean it will travel shorter distances? Hmm, they could use blowguns and crossbows. Slingshots and atlatls.

Oh but then the defence contractor cant pad the books and take tax payers for billions off low powered ammo.

By the way these weapons do work in skilled hands. Shit an atlatl will take down a caribou at full charge.

Chris D

The Russians did this years ago. Should be pretty simple.


Racqia Dvorak

Fire a canceling noise prior to a supersonic projectile. It doesn't matter what the target hears, it's what others in the vicinity can hear.

Sub-sonic projectiles have limited range. They can be heavy sledge hammers or lightweight needles, all are subject to the laws of gravity and will have a 'rainbow' trajectory, but a consistent trajectory equals accuracy.

How loud is the supersonic crack of a needle?


So if the speed of sound is 343 m/s, and we assume the bullet travels at that speed the whole time (somehow overcomes air resistance without breaking the sound barrier, and assuming this will not break the sound barrier on another day with different conditions) then under the effect of gravity, in the first 0.1s (34.3m) the bullet will drop 9.8m/s^2*(0.1s^2)= (9.8/100)m= 9.8cm. I can't imagine why they might have an accuracy problem, with a whole handspan drop in just a bit over a third of a football field. Clearly this is only useful as a very close range. Why don't they switch to energy weapons? A high power pulse diode pumped IR laser could put a nasty hole in someone with minimal noise and the ability to recharge anywhere you can find a decent wall outlet (or a vehicle providing solar or hybrid electrical support). That, or just start filling paintballs with something a little more nasty - I imagine at least half of the SOCOM guys have extensive experience with paintballs already and this gives them access to more customization that DARPA will ever have.

Charles Bosse

Damn fools need to talk to the Russians. They have the VSS "Vintorez" and the VSK and VSSK "Vychlop" weapons.

The VSS is a direct replacement for the AK-47 / AKM series of rifles that have been fitted with silencers. It fires a subsonic 9mm bullet with a solid steel core fitted to a necked down 7.62x39 case. It is capable of defeating body armor out to 400 meters.

For a true silent but deadly sniper weapon, the VSSK is the way to go. Firing 12.7mm solid bronze slugs with an 1 MOA accuracy at 100 meters this weapon would be an ideal for urban campaigns. The weapon is fitted with an integral bipod and silencer.

Catman's Litterbox

Ah. I was going to mention VSK and VSSK. You could also design bullet to become mini-missle, burn fuel - but visible in dark. Cheapskates use "rim-fire" rounds. Lower velocity, much less sound. Requires some scope adjust. Fancy range-finder does trick. Perhaps government should do so rim-fire?


Use a crossbow (or better still, Russian technology).


Rocket propelled bullet with compressed air launch. Not silent but reasonably quiet. Even a crossbow or a slingshot is not silent. Both can be fairly accurate, and deadly.


If the Russian weapons will not do, Gyrojet with a kick starter sub-munition round all sealed flatter trajectory high energy impact at max range with lots of mass available.

Joseph Mertens

Didn't the airplane folks recently solve sonic boom problems on aircraft by modifying the shape? I wonder if a bullet could be shaped to travel supersonic w/out making a boom. Someone straighten me out if I've got this wrong.


Dig through a pile of back issue of American Rifleman, what they want is likely in there somewhere.

Another benefit of a subsonic rifle round is it'll shoot through several feet of water. Supersonic bullets shatter in 2 feet or less, even the mighty .50 BMG.

Just once I'd like to see in a movie where some guy jumps into a river and other guys start blasting away... someone says "No you idiots, pistols! Subsonic bullets go deep in water!" In other words, every movie you've ever seen with rifle bullets shooting past someone swimming underwater has it wrong.

Gregg Eshelman

The problem with crossbows is that they take so much energy and time to reload. A large caliber C02 air rifle with a sound suppressor should work really well.


I thought they were already playing with 50 cal prechargedpneumatics at 900fps. accuracy problems until they change alloys and shapes. I think the shape of the projectile can 'stretch out' the wave of the boom so it is less noticeable. What happened to the micro powered missiles that were supposed to drive by wire ... Solyndra? The Israelis use indelible ink paintballs filled with drop-you-to-your-knees cadaverine (or similar). I like the doped blow dart idea best. The impact of the hit causes it to syringe-in the drug. Maybe they should watch (Crocodile) Dundee 2 for some ideas.

Darick Nordstrom

If you desire quiet, why not use a small crossbow?

Randolph Garrison

All the crossbow enthusiasts please make a crossbow shaped object and then move around your home trying to clear rooms with it. If you have children have them play the op-force with toy guns. See who wins.


A subsonic round in a non-suppressed weapon? AFAIK the 45 cal is usually subsonic and its not silent so yes, law enforcement can and have been using subsonic rounds

Vincent Maldia

Well, you could introduce a rifle with a "gas dumping" gas regulator. That is, have a lever that can reduce the amount of gas going to the projectile. Old muskets used to lose gas out through the flash hole area, so all you'd need in a basic example is a hole, and a slider to adjust the amount of gas loss. This would form as a type of power adjuster, so the amount of force available to the projectile could be reduced to an amount only suitable for subsonic speeds. An ordinary sized rifle projectile at that point may be too small (F=MA) to do sufficient damage, but may be effective at short range.

Another way to look at it might be some kind of staged smart bullet. Most people here know how a hollow point works - it's aerodynamic in flight, and becomes a bludgeon on impact. Well, couldn't that theory be applied in reverse? Imagine a two-stage bullet with poor aerodynamic characteristics in it's first stage. That is, when the projectile is fired, it has poor aerodynamics, then at a predetermined point in flight, the first stage breaks away, leaving an aerodynamic second stage which has been "air braked" down to a subsonic speed by the poor characteristics of the first stage. It might sound a bit tech heavy, but similar things are being developed elsewhere in military technology.

Conor Brannigan

This is not a new "problem" nor is it new research. Frank Barnes of 'Cartridges of the World' fame did a load of research and testing and forwarded it to the US army during the 70s e=when a new 'brushbusting' caliber was needed for special forces in Vietnam. He shortened the redoubtable .458 Win cartridge and got it to work in a semi auto rifle. It went through anything (trees, walls, backpacks and radios) and was sub-sonic. They rejected it. The .30 Wisper is another experimental sub-sonic cartridge that supposedly has accuracy and hitting power. Most of the press releases by these firms doing the research are to justify their 'reinvention of the wheel' and the subsequent cost.


stick a silencer on a 1911 the 45APC is already subsonic. WWII used 45apc in a modified, silenced, LE #4 rifle for special operations. As noted SSK industries has a well tested, line of subsonic ammo, with simple inexpensive refit to M16

Tom Swift
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