Abstract: A rupture mechanism is integrated into a plastic casing used for low velocity projectile rounds. The casing incorporates a cylindrical wall having a top mouth end that fixedly receives a projectile to be launched, and a bottom base head at the bottom end. A low-pressure chamber is formed by a first interior space between the cylindrical wall and the bottom base head. A high-pressure chamber formed on the bottom base head extends into the first interior space. The high-pressure chamber is formed with a second interior space to receive an ammunition cartridge. A top portion of the high-pressure chamber has an integrated burst area wall with a thickness selectively formed based on a type of projectile fixed at the top mouth end. Detonation of propellant gas from the cartridge builds up pressure to rupture the integrated burst area wall with a delay time in rupturing the integrated burst area wall based on the thickness of the integrated burst area wall.