The Quiet Clash of the Sound-Suppressed Submachine Gun World

Affiliate Disclosure: This page contains affiliate links. We earn from qualifying purchases.

Suppressed pistol-caliber submachine guns are highly specialized combat weapons. Movies make them look extra cool. However, I have it on reliable information that movies are not technically real. In the real world, their practical application is markedly more nuanced.

The most illuminated commentary I have found concerning the practical use of suppressed weapons in combat came from Major John Plaster. Major Plaster was a member of MACV-SOG during the Vietnam War. These iron-willed Special Forces commandos did deep penetration missions into Laos and Cambodia most commonly focused on interdicting communist supply lines. They were forever outnumbered and hopelessly outgunned. His book on the subject, Secret Commandos: Behind Enemy Lines with the Elite Warriors of SOG, is a simply magnificent read. You can find it on Amazon.

When Major Plaster first arrived in country, his SOG unit was short on XM177E2 carbines. As a result, he drew a sound-suppressed 9mm Swedish K to carry on his first few trips downrange. The suppressed K-rifle was exotic and looked sexy. The 9mm chambering also meant you could carry scads of ammo. It seemed the perfect tool for a clandestine special ops mission. However, that’s not the way things played out.

Successfully completing these SOG missions was predicated upon stealth. If the enemy discovered you, the school solution was to disengage as soon as possible via overwhelming firepower and call for air support and immediate extraction. The problem was that, when enemy troops were assaulting Plaster’s position they didn’t know they were being fired upon. His quiet 9mm subgun was simply not terribly intimidating. By contrast, the stubby XM177E2 was a fire-breathing dragon that made the devil’s own racket. As soon as one of these Colt carbines came available, Plaster binned the quiet K-rifle and never looked back.

Physics

There yet remains still a very real practical niche for a sound-suppressed submachine gun. In fact, even this deep into the Information Age, the time-tested HK MP5SD is still issued among certain top-tier direct action units simply because it is, relatively speaking, really quiet. That can indeed be a critical attribute in certain narrow circumstances.

There is a great deal of physics behind the noise a firearm makes. The most obvious bit is the sound produced by the gun’s action and the hot, high-velocity gases that are released at the muzzle behind each round fired. Mechanical noise can be mitigated by good weapon design. A quality sound suppressor will capture a great deal of the muzzle chaos. However, the sound made by the bullet once it is outside the gun is beyond the capacity of any mechanical contrivance to influence.

This is an issue with any weapon firing supersonic rounds. Just like a high-performance fighter jet, when that bullet passes the magic threshold of 1,125 feet per second in dry air, it is going to produce a loud sonic crack. The only reliable way to address that is to fire subsonic ammo.

For high-velocity rifles, this really is impractical. A 5.56mm assault rifle will not cycle reliably if you dump enough power to render that diminutive little .22-caliber bullet subsonic. However, that isn’t necessarily the case with 9mm weapons. By adjusting bullet weights, 9mm Para may be loaded to produce either supersonic or subsonic performance. However, subsonic 9mm ammo can be expensive and tough to find. In the military world, that is also one more line item the supply guys have to keep track of. There is a mechanical solution.

By drilling a series of ports in the barrel underneath a sound suppressor, it is possible to craft a gun that will feed standard 115-grain ball ammo but bleed it to subsonic velocities. That way, the gun will run ubiquitous service ammo without producing the annoying sonic crack. There are three production guns that saw relatively widespread service that pulled this off.

The Swedes built an integrally-suppressed version of their Carl Gustav m/45 that incorporated a ported barrel to render standard ball ammo subsonic. The Brits produced a sound-suppressed variant of the Sterling designated the L34A1 that accomplished the same goal. Both of these weapons fired from the open bolt. The closed-bolt HK MP5SD did the same thing using an altogether different method of operation. Each of these three guns has unique strengths and weaknesses.

The Swedish Solution

The Carl Gustav m/45 was called the Swedish K or K-rifle by the American Special Forces operators who used it in Vietnam. Adopted in 1945, the Swedish K was an altogether conventional design. Feeding from a 36-round stick magazine, the K-rifle was full auto only.

The tubular steel stock folded to the right, and the gun came with a removable magwell that allowed the use of bulky 72-round drums. Thusly equipped, the gun maneuvered with the grace of a pregnant hippo. However, with a cyclic rate of fire of 600 rpm, that big fat drum did last a long time.

The gun’s sole safety was a slot that could be used to lock the bolt to the rear. Despite using WW2-era technology, the Swedish K was ridiculously reliable and quick in action. It also looked cool, so the SEALs and SF operators who used it checked that block. The Navy contracted with Smith and Wesson to produce their M76 as a replacement once the Swedes stopped selling the guns to us in protest of the war.

The British L34A1 Sterling

The Sterling was, likewise, a WW2-era contrivance. First field tested in 1944, the Sterling was intended to replace the wartime Sten gun. Despite utilizing the same basic layout, the Sterling was a markedly more refined design. The gun was officially adopted in 1953, and some 400,000 copies were produced.

The Sterling featured a fairly complicated underfolding steel buttstock that is a bit cumbersome to operate but rock steady in use. The gun was selective fire and fed from the finest submachine gun magazine ever created. The 34-round double-column, double-feed Sterling mag featured a pair of roller bearings as a magazine follower. Nothing on Planet Earth is smoother.

The sound-suppressed version of the Sterling included a permanently-mounted integral sound suppressor that incorporated an expansion chamber on the near end. This chamber enclosed a length of barrel through which had been drilled 72 small ports. The cumulative result was to lower the velocity of standard ball ammo to the subsonic range. Like the sound-suppressed Sten Mk IIS that inspired it, operators of the L34A1 were trained to run the gun on semiauto only absent some serious emergency. 

The German MP5SD

The 9mm MP5 first saw service in 1966. Unlike the other two guns we have discussed, the MP5 fired from the closed bolt via a complicated recoil-driven, roller-delayed action. The MP5 fed from a 30-round box magazine and cycled at around 800 rpm.

The MP5 was one of the world’s first truly modular military weapons. By swapping out furniture, buttstocks, and optics, a common MP5 chassis could be used for a variety of applications. Heckler and Koch built somewhere between 700,000 and one million copies. The gun remains in production in several countries today. 

The MP5SD was the integrally-suppressed version of the standard MP5. SD stood for Schalldämpfer or “sound suppressor” in German. The abbreviated 5.7-inch barrel on the SD incorporated 30 ports that also dropped standard velocity rounds to the subsonic range.

The closed-bolt nature of the design made the MP5SD innately stealthier than the Swedish K or L34A1. However, the tradeoff was that the gun was more expensive to produce and there was more stuff in it to break. Regardless, the MP5SD enjoyed a spectacular career with the Free World’s special operations forces that continues to this very day.

One of the reasons for the MP5SD’s popularity was the classic 1990 Charlie Sheen action movie Navy SEALs. In the film, Sheen and Michael Biehn play battle-hardened Nay special operators who travel the globe killing terrorists to make the world safe for democracy. For the first two-thirds of the movie, the SEAL team packs sound-suppressed MP5SD’s.

Practical Tactical

I was blessed to be able to run these three guns side-by-side. The Swedish K is the only one of the three with a readily-removable barrel. Swapping between the standard barrel and the suppressed version involves nothing more than spinning a threaded collar. All that mass reaching so far forward does make the gun fairly front-heavy. However, it is quite controllable as a result.

The L34A1 Sterling is an acquired taste. The left-side magazine makes it much easier to run the gun from the prone, but all that weight hanging off to the side takes a little getting used to. However, the Sterling’s sedate rate of fire and simply magnificent magazine make it easily controllable, even when in a hurry.

The ergonomics of the MP5SD set the standard for everything else. The center of gravity feels about perfect, and the controls are handy and accessible. The bolt must be manually locked back for magazine changes, but that is a perennial crowd-pleaser when executed well. The accelerated rate of fire demands a bit of attention for optimal control, but the roller-delayed action is as smooth as a baby’s butt. There is a reason the MP5SD has enjoyed such staying power across the decades.

On the Internet at least, the Sterling has the reputation for being the quietest production 9mm SMG in the world. However, that has not been my experience, at least with these examples. While the MP5SD and the Swedish K do indeed consistently drop 115-grain bullets to around 900 fps, the Sterling is not so aggressive. Certain lightweight loads can still just peek over the sound barrier through this gun. Interestingly, all three weapons are noticeably more comfortable firing heavy 147-grain subsonic ammo despite their ported barrels. When firing heavy subsonic loads through the MP5SD with the sun at my back I could actually see the rounds zipping downrange.

Ruminations

Everything in life is a tradeoff. Bleeding standard-velocity 115-grain 9mm rounds to subsonic speeds deprives these guns of a great deal of their power. A friend who served in the Ranger Regiment back in the 1980’s had access to a handful of HK MP5SD’s for special applications. He related an inability of the guns to penetrate a steel oil drum at all but intimate ranges. This restricted the gun’s practical utility. 

Zipping around with full auto subguns that make little flatulent noises when fired looks great in the movies. However, reality is not always so clear cut. While there is certainly a niche for a sound-suppressed, pistol-caliber submachine gun in modern covert operations, sometimes the noisy sort make more sense. Regardless, these integrally-suppressed super-sexy subguns do make for a simply splendid way to kill a lazy Saturday at the range. 

---