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BB guns operate on a principle similar to most firearms, as illustrated by Tim Phillips Photos / Getty Images.To grasp how BB guns function, it's essential to start with traditional firearms. The core concept behind nearly every gun, whether a handgun or a cannon, involves generating a small explosion behind a projectile within a cylinder. When the explosion occurs, its expansion is constrained by the cylinder's robust walls, which are stronger than the explosive force. Consequently, the explosion can only expand down the cylinder, known as the barrel. If a projectile, such as a bullet, is present, the expanding force propels it forward through the barrel.
BB guns follow a similar principle to firearms, but without the explosion. Instead, they rely on compressed air, carbon dioxide, or another gas. Before firing, the gas is compressed, increasing its density and pressure compared to the surrounding atmosphere. The compressed gas is stored in a sealed chamber until the trigger is pulled, releasing it into the barrel behind the BB. The higher pressure of the gas propels the BB forward at high speed, overcoming atmospheric resistance. This mechanism powers all gas-operated guns, including air rifles and paintball markers.
Air guns come in various designs, primarily distinguished by their methods of generating compressed air:
- In pneumatic models, you manually pump air to create a reservoir of compressed gas. A lever at the bottom of the gun moves a piston within a tube. Inside the tube, a check valve allows air to enter but prevents it from escaping. Each pump increases the air mass in the reservoir, which has a fixed volume. As the mass grows while the volume remains constant, the air's density and pressure rise with every pump.
- Another popular system is the spring air design. Here, the pump lever compresses a spring by pushing a piston backward. As the piston moves, it engages a small latch, known as a sear, which holds the piston in place, keeping the spring compressed. When the trigger is pulled, the sear releases the piston, allowing the spring to expand and push the piston forward. This action compresses the air behind the BB, generating the pressure needed to fire it.
- Some air guns eliminate the need for pumping by using pre-compressed gas stored in cylinders, similar to a scuba tank. To fire, the gun simply opens a pathway between the gas source and the chamber behind the projectile. One of the most innovative designs is the "pump-action" mechanism found in basic paintball guns.
At the center of the gun lies a long valve tube, extending from the barrel to a chamber at the rear where the gas cartridge is attached. This tube passes through several components, including the bolt, a spring, the hammer, and the valve seat at the gas intake end. While the barrel end of the tube remains open, the openings at the other end are sealed by the valve seat. A cup seal, supported by a small spring and gas pressure, holds the tube in place.
When the gun is uncocked, the bolt blocks the barrel, preventing ammunition from entering. Cocking the gun involves pulling the bolt backward, compressing the spring until the bolt aligns with the hammer. This action achieves two things:
- As the bolt retracts, it opens the ammunition intake, allowing a BB or paintball to drop into the barrel.
- A small sear on the hammer catches the bolt, locking them together so they move as a single unit.
Once the bolt is pulled back, the shooter pushes it forward along with the hammer. To discharge the gun, the trigger is pulled, which lifts the sear's back end, causing the front end to drop. This action releases the hammer from the bolt, allowing the spring to swiftly drive the hammer backward. As the hammer moves, it strikes a raised edge on the valve tube, forcing it backward momentarily. This movement overcomes the forward pressure from the rear spring and gas, exposing the tube's side openings. Pressurized gas rushes through these openings into the barrel, propelling the projectile at high speed.
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