Conditions at the muzzle
The instant the bullet exits the barrel, a charge of propellant gas erupts through the muzzle. Parameters of this charge for .308 Win:
- Pressure: 30–40 MPa (300–400 atm)
- Temperature: 1,500–2,000 K (1,230–1,730 °C)
- Outflow velocity: 800–1,200 m/s
- Gas mass: 3–5 g per shot
Without an MBC this charge expands into open air instantly — that is the gunshot sound and the muzzle flash. Gas energy converts to a shockwave moving at the speed of sound and to infrared radiation.
The MBC intervenes in this process: gas does not expand into open air — it expands into a controlled volume.
What an expansion chamber is
An MBC chamber is a sealed (on the inlet side) internal volume with a single outlet — the bullet hole in the front baffle. Chamber volume is 5–10× the bore volume over the chamber length.
When the bullet passes through the first baffle, gas enters the first chamber. By the adiabatic expansion law (PVγ = const), pressure falls in proportion to volume increase. A rough estimate:
| Parameter | At muzzle | After 1st chamber | After 4th chamber |
|---|---|---|---|
| Pressure, MPa | 35 | 6 | 0.5 |
| Temperature, K | 1,800 | 900 | 350 |
| Velocity, m/s | 1,000 | 400 | 80 |
By the time gas exits the MBC's exit hole it is essentially subsonic, relatively cool, and at near-atmospheric pressure. The sound at this stage is the noise of escaping vapor — not a shockwave.
Turbulence and interference
Beyond adiabatic expansion, a second mechanism operates in the chambers — turbulent mixing. Gas flow inside the chamber spirals, reflects off walls, loses coherence. Part of the acoustic energy converts to heat.
In a properly designed MBC, chambers of differing geometry are tuned so their acoustic resonances cancel each other. This is the same principle as an automotive resonator: sound waves of different frequencies arrive in antiphase and weaken mutually.
This is exactly why an MBC is not «a tube with holes». Each chamber's geometry is the result of CFD computation and bench tuning.
Why titanium and not steel
Gas at 1,800 K moving at 1,000 m/s is a plasma-like flow. It acts as abrasive + corrosive + thermal shock at the same time. 17-4 PH steel under these conditions:
- Oxidises on the walls of the first chamber
- Loses hardness in the muzzle zone after 5,000 rounds
- Accumulates carbon and propellant deposits
Ti-6Al-4V under the same conditions:
- Forms a self-healing TiO₂ oxide film 5–10 nm thick
- Holds strength under thermal cycling thanks to its α+β two-phase structure
- Does not corrode in propellant combustion products
Material deep-dive: Why Ti-6Al-4V Grade 5 is the best material for MBCs.
Video: what happens inside an MBC
How design maps to performance
MBC effectiveness is governed by three parameters:
- Total chamber volume — the larger, the steeper the adiabatic pressure drop
- Number and shape of baffles — they set the path of the gas and how many times it is slowed
- Hole geometry — cones, chamfers, and steps direct the turbulent flow
What this looks like in practice: in the .308 test series of July 2026 our models delivered 28.9 to 35.0 dB of reduction. The spread between them is a difference in working volume and chamber layout: more volume means more reduction, while compact models and integral designs — where part of the length goes over the barrel — trade a few decibels for size. The figure for a given model is on its product page, the full report is at titan-dtk.ru/testzvuka.
Bottom line
An MBC is an acoustic resonator and a thermodynamic trap at the same time. The gunshot's sound does not vanish — it is dispersed in time and converted to heat on the chamber walls. The more precisely the geometry is tuned and the more durable the material, the longer the device retains its rated performance.
An MBC is not a silencer. It is an engineering solution for managing the gas dynamics of a shot.