low recoil

The high-low system, also referred to as the high-low pressure system, the high-low propulsion system, and the high-low projection system", is a design of cannon and anti-tank launcher using a smaller high-pressure chamber for storing the propellant. It enables a much larger projectile to be launched without the heavy equipment typically required for large caliber weapons.
When the propellant is ignited, the higher pressure gases are bled out through vents (or ports) at reduced pressure to a much larger low pressure chamber to push the projectile forward. The high-low system allows the weight of the weapon and its ammunition to be significantly reduced. Manufacturing cost and production time are drastically lower than for standard cannon or other small-arm weapon systems firing a projectile of the same size and weight. It has a far more efficient use of the propellant, unlike earlier recoilless weapons, where most of the propellant is expended to the rear of the weapon to counter the recoil of the projectile being fired.

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