1. What is the purpose of a Suppressor?

A suppressor primarily reduces muzzle blast. This occurs as soon as the projectile leaves the barrel and the high-pressure combustion gases escape abruptly. The effects can be impressively observed in schlieren images:

On the left is a suppressed shot, on the right an unsuppressed one (.300 BLK, supersonic). The video clearly shows how quickly the pressure escapes without a suppressor and how long it is maintained with a suppressor.
Source: youtube.com/@smartereveryday

More high-speed recordings of the muzzle: youtube.com/@BallisticHighSpeed: without suppressor, with suppressor

2. The challenge with self-loaders

Modern self-loading long guns predominantly operate by using gas pressure – this includes gas operated (DI, internal and external piston systems) as well as unlocked or delayed blowback systems, as they also function in a gas pressure-dependent manner. These systems are designed for a defined normal function, usually in the range of 5–6 m/s bolt velocity. Parameters such as gas port diameter, gas port position, piston size, bolt mass, recoil spring, buffer, or receiver geometry are designed to work with these velocities.

If a suppressor is mounted, one crucial factor changes: the gas pressure curve. The maximum pressure does not increase, but the pressure curve is significantly longer. During this time additional time, the self-loading system receives surpus energy. The extent and effects of this functional increase depend heavily on the weapon design – especially the barrel length. Shorter barrels react more sensitively and show greater deviations.

The difference can be determined directly via the bolt velocity or indirectly via the rate of fire or case ejection. AR-15 platforms, in particular, react with visible changes in ejection angle depending on gas pressure.

Many weapons today have adjustable gas blocks and offer a special setting for suppressed operation. This reduces the gas flow and thereby compensates for the prolonged pressure. This corrects the excessive function – but not the so-called blowback.

3. Backpressure & Blowback

A basic distinction is made between two effects:

  • Backpressure – the increased or longer-lasting gas back pressure in the system.
  • Blowback – the escape of gases to the rear in the direction of the shooter.

Image series with Stgw 90 and HK416 illustrate this:

Neither weapon has a special suppressor gas setting. The strong blowback with conventional suppressors is visible, as is the altered case ejection with the HK416. Unsuppressed weapons typically eject at an angle of 120–130°. With a conventional suppressor, the angle is reduced to 45–50°, while RBS systems reach around 90° – i.e., the normal range of approximately 90–130°.

Blowback leads to exposure to combustion gases and heavy metal particles. These are neither harmless nor pleasant – they irritate the eyes and respiratory tract and make shooting more difficult, especially with rapid firing sequences or in enclosed spaces or vehicles.

There are corresponding measurement setups for this. The corresponding NATO standard proposes a closed box to collect the gases. The gas concentration in the box is continuously measured via a gas measuring probe.

Typically, several gases are measured, here exemplarily the carbon monoxide concentration over time.

It is important to note not only the absolute concentration but also the steepness of the increase. Since the probe is positioned where the shooter’s nose would be, a steeper increase means that the gases are blown directly into the shooter’s face.

Important: Blowback and backpressure correlate, but not linearly. A 10% increase in function can cause a 50–100% increase in blowback. Even if there is no increase in function, blowback can occur because residual pressure in the suppressor lasts significantly longer than the time until the bolt opens.

The strength of the effect again depends heavily on the weapon type; short-barreled systems are significantly more affected.

4. RBS – Reduced Backpressure System


The goal of recent and most recent suppressor development history is to reduce blowback and backpressure without sacrificing damping performance. B&T had the first backpressure-reducing suppressor geometry in the MP9-SD in 2004. The MP9/TP9 is a recoil loader that would rather struggle with too little function due to a suppressor on the muzzle. However, the suppressor is not attached to the muzzle but to the housing-fixed barrel jacket. This means that the face of the barrel acts as a piston. The function increases due to the suppressor. The solution was a suppressor with a conventional core and a bypass that directs the gases past the core:

The bypass flow is slowed down much less than the gas flow in the core. Many suppressor designs with a bypass are therefore louder at the muzzle than conventional suppressors. However, due to the “Port Pop” of the noise of the outflowing gases at the ejection port, they are often quieter at the shooter’s ear than conventional suppressors. In order to achieve the best possible coordination, different suppressor geometries are first compared in flow simulations:

This simulation shows suppressors with our QDN lock. This is for standard NATO flash hiders. Since the A2 standard geometry does not seal completely, the QDN has a gas relief at the rear end. If you compare the red-marked flow from the gas relief, you can guess the difference in back pressure. The pressure comparison shows it even better:

Earlier RBS models are shown. Current Print-X simulations are not published for IP protection reasons.

5. Who needs it?


Simply put: all gas pressure loaders.
If you use weapons with gas adjustment in conjunction with RBS-SDs, set them to the “Normal” position, not to the SD position!
A noteworthy exception is gas pressure loaders in 300BLK. Here, the weapons are usually delivered ex works with a gas setting for subsonic and supersonic ammunition. Most 300BLK weapons known to us are tuned to function with conventional suppressors. In the combination RBS + subsonic, this often leads to underfunction.

An exotic example would be miniguns. Here, the suppressor has no influence on the function, as the weapon is electrically driven. However, the phenomenon of blowback is still very much present. Good to see in this video: Youtube/TFB

6. Who doesn’t need it?


Especially repeating rifles. Regardless of whether cylinder, straight-pull or lever-action, repeaters do not need RBS. There is no influence on the function. Blowback does not occur because the bolt is not opened quickly enough even with rapid repeating