HPA systems are unique gas systems which have a lot of advantages as well as disadvantages. While the above might paint HPA systems as the dominant choice within airsoft, there are a number of drawbacks associated with the systems, which we will address later. However, for now, just look at HPA systems as a rifle that is traditionally powered by an external canister of pressurised air. That said, newer systems are emerging on the market that allows HPA systems to be used in conjunction with Co2 cartridges or a tank which attaches directly to your Airsoft Guns as well as your BB Guns.