The principle of the BB gun is very similar to the principle of a firearm, but there is no explosion. Its expanding material is ordinary air, carbon dioxide or some other gas. Prior to launch, the gas will be compressed to increase its density to achieve a higher gas pressure than the gun's external environment. The compressed gas is stored in a closed container before the trigger is pulled. When the trigger is pulled, the gas container will open and the gas will flow into the barrel space of the BB gun. As the gas is compressed, the BB gun's gas will have a greater thrust than the ambient air, causing the BB to push the gun at high speed. This principle is used for all pneumatic guns, including high-pressure rifles and paintball guns.

The middle of the gun is fitted with a long valve tube. This valve tube extends from the barrel to the barrel of the gas cylinder connected to the rear of the gun. Along this path, the valve tube passes through the bolt, the spring, the hammer, and the valve seat at the rear of the gun. At the end of the barrel, the valve tube remains open at all times. 

The other end is located at the opening on both sides of the valve tube and is blocked by the surrounding valve seat. The valve tube is fixed by a cup seal. The sealer uses the small spring behind and the gun pressure to hold the valve tube. When not in the ready-to-go state, the bolt protrudes into the barrel to prevent the ammunition from entering. To enter the ready state, the shooter pulls the bolt back and presses the spring to hold the bolt against the hammer.