Co2 airsoft guns are airsoft weapons that use 12 gram Co2 cartridges to propel airsoft pellets and reset the action. These cartridges are about $0.50 and can be found anywhere from sporting goods stores to Walmart. Each cartridge gives players about forty shots and must be replaced with a new cartridge every time they run out.
Most gas airsoft weapons are pistols due to the limited amount of shots each cartridge provides. The pistols that aren't Co2 are normally spring guns which all need to be manually re-cocked. Co2 airsoft pistols have the advantage of being semi-automatic as well as being more powerful than spring pistols.
Another advantage of gas airsoft weapons are their realistic look and feel. Many gas airsoft guns have realistic magazines with both the pellets and Co2 cartridges in the same magazine, so that when the gun runs out of either pellets or Co2 you just replace the magazine just like you would in a real gun. All gas guns also have realistic recoil and are of all metal construction in order to handle the pressures of the Co2.
Although Co2 guns have their advantages, they also have disadvantages. On very hot days, Co2 airsoft guns will perform extremely well and outperform nearly anything, but on cold days Co2 airsoft guns will be very inconsistent and may not even fire. This is because Co2 expands on hot days, but becomes a very cold liquid in cold conditions. Co2 airsoft guns cannot use the liquid Co2 to propel the pellets very well and so they malfunction. It also can become a chore to replace Co2 cartridges in the middle of a heated airsoft battle.