Silencer Terms and Tech, Part 2

To read Silencer Terms and Tech, Part 1, click here.

Hollywood movies often portray pistol silencers as slightly larger than a toilet paper tube. The high pitched squeak of the shot sounds like a sneaker on a basketball court when the movie star shoots his gun. In reality, most pistol silencers are about as long as the gun to which they are mounted, and sound more like an air hammer or disconnecting the hose from an air compressor. Many centerfire caliber silencers do not even reduce the noise level enough to allow the shooter to safely discard ear protection. Also, a silencer can only affect the noise generated by the muzzle blast of the shot. The gun’s action cycling, the supersonic crack of the bullet traveling through the air (unless using subsonic ammunition), and even the sound of the bullet impacting the target downrange add more sound than most people realize. That’s certainly more sound effects than movie directors can be bothered to include.

Mk22 Mod 0 “Hush Puppy” 9mm

During the Vietnam era, the Navy’s Mk22 Mod 0 “hush puppy” pistol cleverly tackled the problem of slide cycling noise. Starting with a 9mm S&W Model 39, the slide stop lever on the gun was modified so that if the shooter held it down, it would engage the slide notch with the slide still shut. This action lock held the slide closed and turned the pistol into a one shot weapon. By releasing the lever, the slide could be cycled by hand after each shot to rechamber the weapon. This was very effective at making the Mk22 Mod 0 one of the quietest silenced 9mms of its day, but it was awfully hard on the slide stop lever and slide notch, which wore prematurely over the lifespan of the pistol. The Mk22 was called the “hush puppy” to give the impression that it was meant for shooting sentry dogs. Though the Vietnamese rarely used dogs, somehow the hush puppies were heavily utilized by Navy Special Forces anyway.

The wipe design is another piece of silencer tech from the Vietnam era. Instead of baffles, the original Ingram Mac-11 silencer used wipes, which were solid disks made of rubber or felt and separated by washers. The hole in the middle of each wipe was sealed off temporarily by the bullet as it flew through the envelope and physically touched each wipe. In theory this meant that the propellant gas was temporarily trapped behind the bullet and wipe, so the wipe would act as an efficient baffle. In reality it meant a loss of accuracy, melted chunks of wipe flying downrange, and a silencer that performed pretty well during the first magazine and hardly at all by the third one. The gooey mess of destroyed wipes had to be replaced to make the silencer work again.

Replaceable wipes for original M11 silencer

A later development was the integral silencer design, in which the envelope entirely covers up its host barrel. The barrel is ported with many holes corresponding with the positions of the baffles inside the envelope. Each hole in the barrel lets propellant gas escape to be trapped by the baffles. The integrally silenced Mp5SD 9mm submachine gun is legendary for being nearly “Hollywood quiet” when fired. Part of the reason is that the integral suppressor design bleeds off the velocity of the fired round due to all the gas escaping from the thirty (yes, thirty!) barrel ports. The round leaves the gun without breaking the speed of sound, eliminating the supersonic crack of the bullet passing through the air and making the sound of firing even quieter.

The Nielsen Device, or recoil booster, is a relatively new addition to silencer design technology.  In most pistol designs for calibers larger than .380acp, the barrel unlocks the gun’s action by moving rearward and tilting (or rotating, for you Beretta PX4/Cougar fans) inside the slide. In the old days, silencing these pistols caused them to lose reliability for two reasons. First, with the silencer attached the barrel effectively weighs much more than normal. Second, the pressure of the propellant gas hitting the baffles inside the silencer acts like a muzzle brake, pushing the silencer and barrel forward. As a result the action would not unlock correctly and silenced pistols were a nightmare of reliability problems.

The solution to this problem was a muzzle mount and spring assembly built into the expansion chamber area of the silencer, behind the baffles. The barrel is attached to this mount and the rest of the silencer can slide back and forth on it like an old fashioned telescope, with the spring holding everything in place until the pistol is fired.  When shooting, the propellant gases pull the silencer forward like before, but they only pull against the spring pressure instead of the whole barrel. The silencer envelope and baffles slide forward on the muzzle mount while the barrel unlocks the action as normal. The invention of the Nielsen device greatly improved the reliability of silenced pistols and it is now considered a must for shooting a pistol with a tilting or rotating barrel.

Nielsen device removed from the expansion chamber of a pistol silencer

The Nielsen device should not be used on a pistol with a fixed barrel, such as an HK P7, or on a rifle. Since the barrel on these firearms doesn’t move, all of the energy of the recoil booster acts like a slide hammer thumping the silencer forward against its own parts with each shot. Eventually the weakest part will break.

The past 100 years have seen a lot of progress in silencer technology, but Hiram P. Maxim would still easily recognize the grandchildren of his 1909 silencer designs. Although improvements in manufacturing techniques and problem solving additions such as the Nielsen device make today’s silencers far more effective than designs from only a few years ago, the principle of operation has remained the same, and so has the goal—making shooting as quiet as it can be! The author would like to thank the following companies for their assistance in writing this article: Advanced Armament Company 2408 Tech Center Parkway Suite 150 Lawrenceville, GA 30043 GEMTECH P.O. Box 140618 Boise, ID 83714-0618

The Mission of Cheaper Than Dirt!'s blog, The Shooter's Log, is to provide information—not opinions—to our customers and the shooting community. We want you, our readers, to be able to make informed decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (3)

  1. I guess I did say “a later development”. Bad transition, I meant the Mp5SD was a later development, not the integrally suppressed concept. Cheers!

  2. You are correct Gregory! I simply didn’t have room to include everything I wished to, but I wanted to at least hit the highlights and for me the Mp5SD is the quintessential integrally suppressed firearm. The DeLisle is way cool too, I hear that someone is making a modern clone now but I can’t remember who it is, NFA Investments maybe?

  3. Your article seems to imply that integral suppressors were a post-Vietnam development which is categorically false. The British Welrod pistol and the DeLisle carbine, both used in WWII, and the British Sterling-Patchett Mk. V (L34A1) submachine gun are all integrally suppressed and predate Vietnam.

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