UNDERSTANDING ABOUT DWELL TIME IN FIREARMS

 

Understanding About Dwell Time in Firearms

Dwell Time: It is the amount of time the gases from the fired cartridge are acting on your actual system after the trigger is pulled.

After firing, the rapidly expanding gases created by the burning propellent exert pressure on the base of the bullet, forcing it down the barrel. After the bullet pass through the gas port, the tapped gas will cycle the action. The bullet must stay in the barrel long enough after passing the gas port to allow sufficient pressure to build and ensure a complete cycle.

GAS PORT LOCATION AND DWELL TIMES:

·       Gas Port Closer to the Chamber (Shorter Dwell Time): When the gas port is closer to the chamber, the bullet passes it earlier in the barrel’s length. This results in a shorter dwell time because the bullet exits the barrel shortly after passing the gas port.

·       Gas Port Farther from the Chamber, Closer to the Muzzle (Longer Dwell Time): If the gas port is located closed to the muzzle, the bullet takes more time to reach it, and there is more dwell time after bullet passes the gas port before it exits the barrel.

LONGER DWELL TIME AND SHORTER DWELL TIME:

Longer Dwell Times:

In longer dwell time the bullet takes more time to pass the gas port from the throat of the chamber, because the gas port is closer to the muzzle, after passing the gas port the gasses are goes to the entire bolt carrier group for cycling the action. The time delay between the chamber to gas port is high because the gas port is near the muzzle.

In contrast, longer dwell times can lead to slower cycling. While a longer dwell time may increase pressure and bullet velocity. It can also delay the operation of the firearms mechanism, potentially reducing the cyclic rate. The system needs time for the gases to act because the bullet travels to long distance to reach the gas port. Which can slow down the overall rate at which rounds are fired.

Increased Pressure and Velocity: Longer dwell times allow more time for gas expansion behind the bullet, potentially increasing the velocity and energy as it exits the barrel.

Improved Stability: A longer dwell time can contribute to greater stability in the bullets flight path, leading to improved accuracy, especially at longer ranges.

Shorter Dwell Times:

In shorter dwell time the bullet takes less time to pass the gas port from the throat of the chamber, because the gas port is closer to the chamber, after passing the gas port the gasses are goes to the entire bolt carrier group for cycling the action. The time delay between the chamber to gas port is less because the gas port is near the chamber.

With shorter dwell time, the gas port is closer to the chamber, allowing the gas pressure to act on the operating system for a shorter period. This means the bolt or piston can start moving sooner after the bullet passes the gas port. The action cycles more quickly, which helps the bolt unlock, extract the spent casing, eject it, and chamber a new round faster than a system with longer dwell time. But here may be the sudden peak pressure due to the ignition of primer will cause over gas problems because of the smaller distance between the chamber pressure and gas port.

Faster Cycling: Shorter dwell times can lead to faster cycling of the firearms, action, which can be advantageous in rapid fire scenarios, such as in fully automatic or tactical weapons.

Reduced Heat Build Up: Less time in the barrel can result in lower heat accumulation, which can prolong barrel life and maintain consistent performance.

DWELL TIME FORMULA:

The dwell time (T) can be estimated as follows:

T = L / V

Where:

T = Dwell time in seconds.

L= Distance from the gas port to the muzzle.

V= Bullet velocity (in meters per second or feet per second)

Example Calculation: A rifles gas port to muzzle distance is equal to 0.7 meters and the bullet velocity is 900 meter per second.

Using the above formula:

T = L / V = 0.7 / 900 = 0.00077 seconds.

ADVANTAGES OF HIGHER DWELL TIME:

·       Increased Reliability: Higher dwell time allows for more consistent gas pressure, improving the cycling reliability of the action, especially with various ammunition types, including lower pressure rounds.

·       Smoother Operation: The extended time for gas pressure to act to a smoother cycling process, reducing the likelihood of malfunctions such as failures to extract or eject.

·       Better Performance with Suppressors: Firearms with higher dwell times can work more effectively with suppressors, as the increased gas pressure helps maintain reliable cycling even under the backpressure created by the suppressor.

·       Reduced Mechanical Stress: A slower cycling action can decrease mechanical stress on components, potentially extending the lifespan of parts like the bolt and carrier group.

·       Improved Accuracy: More controlled gas pressure can lead to better consistency during firing, enhancing precision, especially in precision shooting scenarios.

ADVANTAGES OF LOWER DWELL TIME:

·       Faster Cycling: Lower dwell time results in quicker cycling of the action, enabling a higher rate of fire and faster follow up shots, beneficial in competitive shooting and tactical situations.

·       Reduced Action Delay: With less time for the gas pressure to act, the rifle can reset for the next shot more rapidly, minimizing delays between shots.

·       Compatibility with Higher-Pressure Ammunition: Lower dwell time often pairs well with higher pressure rounds that generate sufficient gas to cycle the action effectively, maximizing performance.

·       Less Gas Buildup: A system with lower dwell time can minimize gas accumulation in the action, leading to reduced fouling and easier maintenance.

·       Improved Control: The ability to fire quickly with lower recoil impulse can enhance control and accuracy, especially in dynamic shooting environments.