10-03-2015, 11:25 AM
Most of the higher power and larger caliber (non PCP) air guns use a gas piston. It's easier to quote from the web:
"Welcome to the new world of break barrel Gas Piston mechanism. At the heart of this new technological break-through is a nitrogen filled gas piston, instead of a coiled steel spring. The Gas Piston Short Stroke will not be adversely affected by temperature and allows for much easier cocking force.
These airguns can be cocked for long periods of time without degrading or losing velocity, like steel springs.
Gas Piston technology dramatically reduces felt recoil by eliminating the double hit and spring torque associated with steel spring guns. While reducing recoil, gas piston airguns are generally much quieter than their spring counterparts. Some manufacturers claim as much as 70% noise reduction compared to spring air rifles.
Many manufacturers utilize gas piston technology including Crosman with their patented Nitro Piston™ technology, Gamo with their IGT (inert gas technology), Hatsan Vortex gas airguns, and Umarex has also recently announced that they will start using gas pistons in some of their air rifles."
Usually these guns are loudest if you shoot lighter pellets that break the sound barrier as the pellet creates a mini sonic boom. If you shoot lead pellets its usually not a problem. Also the gas piston rifles get quieter after continued use when the parts get broken in. They also become more accurate.
ETA: accuracy
"Welcome to the new world of break barrel Gas Piston mechanism. At the heart of this new technological break-through is a nitrogen filled gas piston, instead of a coiled steel spring. The Gas Piston Short Stroke will not be adversely affected by temperature and allows for much easier cocking force.
These airguns can be cocked for long periods of time without degrading or losing velocity, like steel springs.
Gas Piston technology dramatically reduces felt recoil by eliminating the double hit and spring torque associated with steel spring guns. While reducing recoil, gas piston airguns are generally much quieter than their spring counterparts. Some manufacturers claim as much as 70% noise reduction compared to spring air rifles.
Many manufacturers utilize gas piston technology including Crosman with their patented Nitro Piston™ technology, Gamo with their IGT (inert gas technology), Hatsan Vortex gas airguns, and Umarex has also recently announced that they will start using gas pistons in some of their air rifles."
Usually these guns are loudest if you shoot lighter pellets that break the sound barrier as the pellet creates a mini sonic boom. If you shoot lead pellets its usually not a problem. Also the gas piston rifles get quieter after continued use when the parts get broken in. They also become more accurate.
ETA: accuracy