HPA really is making a big comeback as more products for airsoft are coming out to utilise the compress air as power source. The latest is Wolverine Airsoft with their SMP technology... "The Wolverine Airsoft Single Moving Part (SMP) system is the next step in the evolution of HPA airsoft technology. The SMP is the first product to hit the airsoft market which departs from the model of repackaging paintball electro-pneumatic technology to fit into an airsoft gun body.