Conventional wisdom dictates that semi-automatic pistols without fixed barrels (i.e. ones with some flavor of short recoil operated system) require a Nielsen device or “booster” to function with a silencer attached to the barrel. Without a booster the mass — the inertia — of the silencer hinders the barrel’s rearward movement under recoil and the pistol doesn’t reliably cycle.
Well, conventional wisdom sucks and the future of pistol suppressors is boosterless.
Make a silencer light enough — under approximately five ounces — and it’ll run without a Nielsen device. At least on the vast majority of pistols.
Many pistols will run reliably with closer to six ounces fixed to the nose of the barrel (weight limits for a direct-thread silencer is something I’ll play around with soon).
This AB Suppressor F4, for instance, weighs a hair under 4.5 ounces and I have yet to find a single 9mm pistol that doesn’t cycle absolutely, 100% flawlessly with the F4 threaded directly onto the barrel.
It cycles my SIG P365 with a True Precision threaded barrel even with lightly-loaded, 115 grain range ammo and with various subsonic ammo. It’s also cycled nine or 10 other pistols of various sizes and locking mechanism designs with every ammo I’ve tried.
Even the Palmetto State Armory 5.7 ROCK cycles with it attached, and it’s a 5.7×28.
This is the future of pistol suppressors. Lightweight, direct-thread designs that don’t require a booster.
AB’s F4 technically isn’t the only one that’ll run without a booster (JK Armament’s 105 series performs this trick as well, though really needs to be shot “wet” for proper suppression performance), and it wasn’t the first (I’d likely credit the GEMTECH Aurora with that, though the F4 is the first one of modern design that I know of, whereas the Aurora used rubber wipes stuffed with petroleum jelly), but my prediction is that it’s going to be far from the last.
Fixed-mount silencers designed for use on Browning-style short recoil-operated, semi-auto pistols will be the next big thing in pistol suppression.
At this point if you’re thinking, “Okay, sure, cool, sounds fine, but who cares? Why not just run a booster?” Let’s dive into some of the issues with pistol boosters . . .
Booster assemblies add weight. Most of ’em weigh about five ounces. That’s more than the entire AB F4 silencer. The booster assembly itself accounts for more than half the weight of quite a few other pistol suppressors.
Booster assemblies add length. On average, you’re looking at about 1.5 inches of additional length over a similar silencer designed from the get-go to be direct-thread.
Booster assemblies add cost and complexity. They’re typically made from four or more components, a couple/few of which are threaded, precision parts. The piston and spring have to reciprocate inside of the assembly while locking back up so precisely that it doesn’t affect suppressor alignment. Canting the muzzle of the silencer just a few thousandths of an inch out of alignment with the barrel can cause baffle strikes — bullets impacting silencer internals instead of passing cleanly through the bore.
Booster assemblies increase the risk of baffle strikes.
The obvious reason is tolerance stacking — assembling multiple parts in series adds (“stacks”) the tolerance window for each into the final assembly’s effective tolerance range. For example, if the piston has an acceptable tolerance off of perfect of +/- 0.001″ (one thousandth of one inch), and so does the piston collar and so does the booster housing and so does the silencer body, it’s possible that screwing all of those things together lands you 0.004″ (four thousandths) off. Maybe that’s off-center, maybe that’s at an angle, but any amount at any vector taking you away from perfectly concentric with the bore of the barrel is a bad thing. Now that we’ve stacked some +/- fudge factor into the mounting system we have to open up the bore of the silencer more than we might otherwise have to in order to ensure the bullet can pass through it without touching. The bigger the bore diameter in comparison to the bullet diameter, the less efficient the suppressor gets. A direct-thread suppressor like the AB F4, where the mount is integral to the silencer body and there are zero moving parts, eliminates tolerance stacking. The entire bore of the silencer, from muzzle to mount, can be cut via wire EDM in a single operation and will be flawlessly, perfectly concentric in every way (they then cut one set of mounting threads instead of four or five).
For the entire time during which the piston is pulled, by any amount, out of the booster housing by the pistol’s cycling, the silencer is free to wobble. It’s only secure in its alignment when the piston is fully seated inside the housing. If you’re firing rapidly, it’s possible to sort of “outrun” the booster and fire a subsequent round while the piston isn’t fully seated. In some cases, the piston must be in a particular orientation to fit down onto a lug(s) in the bottom of the housing and can come out of orientation during firing, preventing it from fully seating. In either case, baffle strikes are not just possible, but likely. I’ve done this myself on three different 9mm silencers by simply shooting too rapidly.
Booster assemblies increase blowback. With the inside of the booster housing acting in almost all cases as somewhat of a gas expansion chamber and a simple slip fit between piston and piston collar, a jet of gas is often sent directly toward the shooter via this gap.
High pressure gases trapped inside of the housing also increase blowback through the pistol’s action once it opens up and becomes the path of least resistance for this gas to escape. Low backpressure and “flow-through” designs will be more effective when built into direct-thread silencers rather than Nielsen device-equipped silencers.
Finally, booster assemblies create a strange and different recoil impulse. Shooting a direct-thread can like the AB F4 doesn’t; it feels totally normal (i.e. it shoots how it shoots when unsuppressed).
If you’ve shot a suppressed pistol, you’re familiar with the strange “ca-chunk” added to the recoil impulse. Upon firing, the pistol’s rapidly-recoiling barrel launches rearward so quickly that the inertia of the silencer keeps it stationary while the barrel pulls the spring-loaded piston (which is what the barrel is directly attached to) rearward out the back of the booster housing.
At approximately the moment when the pistol’s slide hits its rear travel stop, the piston spring sucks the silencer rearward, effectively returning the piston into the booster assembly. Usually the slide has just begun its trip forward, back into battery, when the suppressor completes its short and fast journey rearward. You can feel this bottoming out of the piston into the housing during the pistol’s recoil cycle.
Then, as usual, the slide continues moving forward until the barrel snaps back into however it locks up with the slide and then hits its forward travel stop, fully in battery. This also sharply stops the suppressor that was along for the ride. If the suppressor is heavy enough, the piston may very slightly extend from the booster again before the spring locks it all up again.
Combine the timing of the slide cycling with the different timing of the piston cycling with the disjointed, delayed movement of the suppressor and you end up with weirdness. This double-recoil ca-chunk thwump feels odd and makes it harder to be fast, accurate, and consistent. It causes a less predictable nose dive of the pistol when it returns to battery. Did I mentioned it just plain feels weird?
In part because a boosterless suppressor must be lightweight and in part because the suppressor moves as one with the barrel, shooting a handgun with a silencer like the F4 on the end feels nearly identical as shooting one without. The biggest difference is that you’ve moved your hearing protection from your ears to the gun.
For all these reasons and more, lightweight, direct-thread silencers are the future of pistol suppression.
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