Silencer Saturday #368: Breaking Down Nielsen Devices
Welcome back to TFB’s Silencer Saturday brought to you by Yankee Hill Machine, manufacturers of the new YHM R45 Multi-Host Suppressor. This week we are looking at the Nielsen device. We have some slow-motion videos demonstrating how it works, and some background discussion to set the stage. Let’s dig into it.
Silencer Saturday @ TFB:
- Silencer Saturday #367: What Is Haynes 282 & Why Is Everyone Using It?
- Silencer Saturday #366: SHOT Show Suppressor Roundup
- Silencer Saturday #365: New Angstadt Arms Suppressors at SHOT 2025
- Silencer Saturday #364: New Design From Contra Cans
- Silencer Saturday #363: YHM Victra 12 Shotgun Suppressor
A few months ago the murder of healthcare CEO Bryan Thompson made silencers front-page news. Suppressors are seldom used in crimes in the United States, and seeing what appeared to be a silencer used in the now-infamous security camera footage sparked all kinds of discussions. Theories about the manual operation of the pistol ranged from plausible to ridiculous, even among purported firearm “experts.” Very quickly the consensus that emerged among knowledgeable people was that the murder weapon's silencer did not have a functional Nielsen device.
Most people use “booster” as an interchangeable term with Nielsen device, sort of like silencer and suppressor. Muzzle or recoil boosters existed long before they were used in silencers. Those boosters harnessed the energy of the gun firing to increase the recoil force to aid in cycling. A classic example of this is the MG-42 machine gun, which uses a muzzle booster to trap pressure and increase the rate of fire.
Like a machine gun muzzle booster, a Nielsen device improves function by its action on the end of a barrel. Semiautomatic handguns typically use a Browning-style locking breech with a tilting barrel. With the gun loaded and in battery, the slide and barrel lock together and are parallel. As the gun fires the barrel remains locked to the slide just long enough for the pressure to drop, then the barrel tilts out of the way and the slide moves to the rear. The barrel pivots right about the chamber with the muzzle pointing up.
This whole process happens very quickly, but if you manually cycle your handgun (obviously make sure it is unloaded first!) it is fairly easy to see. It's more obvious on some handguns than others and is especially obvious on pistols with longer barrels. More than a few times I have had a less-informed customer at the gun counter express alarm that the barrel was not pointed straight ahead.
Not all handguns use this system, though. Some popular manufacturers like Walther (with the PPK) and Beretta (with basically all of their metal-frame pistols) use a fixed barrel. The famous HK P7 also has a fixed barrel. Others use a rotating barrel, like the Beretta PX4 or Keltec PR57. But the vast majority of centerfire pistols use a tilting barrel.
This system obviously works well, but the recoil force of the shot, the weight of the barrel and slide, and the recoil spring must all balance for reliability. Adding the weight of a silencer onto the muzzle throws that balance off and usually causes malfunctions. Sometimes, if a silencer is light enough, it can all still work. But in most cases, the extra weight turns the pistol into, effectively, a manually-operated single shot.
Nielsen devices are a clever way of attaching the silencer to the barrel while decoupling its inertia during the recoil sequence. A threaded piston screws onto the threaded barrel of the pistol, and is captive inside the silencer. A spring surrounds the piston and enables it to slide forward and aft along the bore axis. This allows the suppressor to remain somewhat stationary while the barrel moves. Most commercial silencers also offer a fixed barrel spacer that replaces the spring for use on fixed barrel guns. Here are some pictures of the piston assembly broken down to show the component parts:
With that background laid out let’s turn to the video. I am working on a review of some FN pistols including the FNX-45. It seemed wrong to shoot that pistol without a suppressor so I used my trusty old Octane 45 to put some rounds through it. That provided a nice opportunity to film the operation of the booster assembly, and to show what happens when the booster is disabled. Without further ado, here is the video:
Watch the junction between the barrel and the suppressor. As the gun cycles the piston extends out of the suppressor body, and the spring pulls it back in as the gun returns into battery.
And here is one with the spring removed and the fixed barrel spacer installed:
Note that the slide and barrel unlock, but there is simply not enough energy to cycle fully. The brass did not eject in this video, nor any of the other times I tried it. Even the force of the 230-grain .45 ACP bullet was not enough to overcome the mass of the suppressor.
Here are some still pictures of the operation cycle that show the piston’s movement:
Hopefully this helped to explain the function of a Nielsen device while showing it in action, and in inaction. Thanks for stopping by and we will see you next week.
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AKA @fromtheguncounter on Instagram. Gun nerd, reloader, attorney, and mediocre hunter.
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Thanks for that! I shoot mostly revolvers, so I don't have a pistol suppressor yet & I've wondered what the piston device was actually doing.